Research in Developmental Disabilities 40 (2015) 11–18
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Research in Developmental Disabilities
Gender and geographic differences in the prevalence of reportable childhood speech and language disability in Taiwan Yen-Cheng Tseng a, Der-Chung Lai b,c, How-Ran Guo d,e,* a
Department of Business Administration and Language Education Center, Chang Jung Christian University, Tainan, Taiwan Department of Physical Medicine and Rehabilitation, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chia-Yi, Taiwan Department of Senior Citizen Service Management, Chia Nan University of Pharmacy & Science, Tainan, Taiwan d Department of Environmental and Occupational Health, National Cheng Kung University, Tainan, Taiwan e Department of Occupational and Environmental Medicine, National Cheng Kung University Hospital, Tainan, Taiwan b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 13 October 2014 Received in revised form 5 January 2015 Accepted 28 January 2015 Available online
Speech and language disability (SLD) is not uncommon in children. However, data at the national level are limited, and geographic differences are seldom evaluated. Starting from 1980, the local governments in Taiwan has begun to certify disabled residents for providing various services and report cases to the central government according to the law, and the central government maintains a registry of reported cases, which provides a unique opportunity for studying SLD at the national level. Using the registry data from 2004 to 2010, we calculated the prevalence of SLD by age, gender, and geographic area and assessed the changes over time. Because the government discourages the certification under 3 years of age, we excluded cases under 3 years old from the analyses. We found that from 2004 to 2010 the registered cases between 3 and 17 years old increased from 1418 to 1637 per year, and the prevalence generally increased every year in all age groups except in 12–14 years of age. In each year there were more boy cases than girl cases, and the prevalence rate ratio increased from 1.50 to 1.83 (p < 0.05 in all years), with an increasing trend over time (p < 0.01). A higher prevalence was observed in the rural areas over the years, and the prevalence rate ratio increased from 1.35 to 1.71 (p < 0.05 in all years), with an increasing trend over time (p < 0.01). Further studies identifying the risk factors contributed to the increases might help the prevention of SLD in the future. ß 2015 Elsevier Ltd. All rights reserved.
Keywords: Speech and language disability Impairment Prevalence Registry Gender Geographic distribution Taiwan
1. Introduction Speech and language disability (SLD) is a cluster of developmental disorders that may affect a person’s ability in communication, which is important in school performance, career development, and daily social life. According to the American Speech–Language-Hearing Association (2014), a speech disorder is characterized by having problems with voice or the inability to produce speech sounds correctly or fluently, and a language disorder is characterized by having trouble understanding others or sharing thoughts, ideas, and feelings completely. SLD can be developed in both children and
* Corresponding author at: Department of Environmental and Occupational Health, National Cheng Kung University, 138 Sheng-Li Road, Tainan 70428, Taiwan. Tel.: +886 6 2353535/5802; fax: +886 6 2752484. E-mail address: [email protected] (H.-R. Guo). http://dx.doi.org/10.1016/j.ridd.2015.01.009 0891-4222/ß 2015 Elsevier Ltd. All rights reserved.
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adults, but the reported prevalence ranges widely. For example, the Second National Sample Survey on Disability of China on 2,526,145 individuals found the prevalence of speech disability was 0.53% in 2006 (Zheng, Zhang, Chen, Pei, & Song, 2008), but a house-to-house survey of 10,147 families in rural communities in the north of the West Bank found the prevalence of speech disability was as high as 11.4% around the same time (Hamdan & Al-Akhras, 2009). In the United States, it was estimated that 5% to 8% of preschool children were affected by speech and language delay (US Preventive Services Task Force, 2006). In addition to differences in the incidence of SLD, the large variation in the reported prevalence across studies may be attributable to differences in the case definition, age range, and case finding method (Durkin, 2002; Karbasi, Fallah, & Golestan, 2011). When developed in the childhood, SLD has a larger impact and may persist into later life (American Speech–LanguageHearing Association, 2014; Glogowska, Roulstone, Peters, & Enderby, 2006; US Preventive Services Task Force, 2006), and therefore it is a great concern of parents. For example, in a study of Australian children aged 4–5 years, 25.2% of the parents had concerns about the expressive language ability of their children and 9.5% had concerns about their receptive language ability, which led to accessing speech–language pathologist (SLP) services in 14.5% of the children (McLeod & Harrison, 2009). SLD is not uncommon in children, but geographic differences in terms of urbanization are seldom evaluated. Even though the number of related studies is limited, the results are inconsistent. While a survey of 10,147 rural families in the West Bank found a high prevalence of speech disability as 11.4% (Hamdan & Al-Akhras, 2009), a survey of 25,196 rural families in Pakistan found the prevalence of speech delay was only 0.047% (Ibrahim & Bhutta, 2013). A study compared 100 children 1–60 months old each from two suburban and one urban communities of Mexico and found the prevalence of language failure was higher in one of the suburban community (22%), while the other two had the same prevalence of 13% (Guadarrama-Celaya et al., 2012). However, the number of participants was small, and the difference did not reach statistical significance. According to the Disabled Welfare Law (1980), the local governments in Taiwan certify the disabled residents and provide various services, and the Ministry of Health and Welfare maintains a registry of reported cases. The Department of Statistics of Ministry of Health and Welfare (2014) publishes summary data each year and the registry data of Taiwan present a rare opportunity for studying the epidemiology of SLD at the national level. In a previous study, we analyzed the data and found a constant increasing trend in the prevalence of SLD from 2000 to 2011 (Lai, Tseng, & Guo, 2013), but we did not compare SLD between the two genders or evaluate the geographic difference. Therefore, we used the data from 2004 to 2010 to assess the changes in prevalence, gender, and geographic differences of SLD in Taiwanese children over time. 2. Methods 2.1. The disability registry system in Taiwan The promulgation of the Disabled Welfare Law in 1980 is a milestone in the history of promoting disability registry in Taiwan. The categorization system covered seven types of disabilities (SLD, visual impairment, hearing impairment or balance disability, disability of limbs, intellectual disability, multiple disabilities, and other disabilities listed by the Department of Health) initially (Disabled Welfare Act, 1980), and nine other types were added from 1981 to 2001 (Physically and Mentally Disabled Citizens Protection Act, 2001). ‘‘Multiple disabilities’’ means the concurrence of two or more disabilities (Department of Health, 2008). According to the law, the local governments began to certify disabled residents and provide various services in 1980, and patients with disabilities can make applications for certification through the local government office in their residential areas. The local governments report cases to the central government, and the Ministry of Health and Welfare maintains a registry of reported cases. We have adopted the registry data to conduct a series of studies on developmental disabilities (Lai, Tseng, & Guo, 2011; Lai, Tseng, Hou, & Guo, 2012a, 2012b; Lai et al., 2013; Lai, Tseng, Lin, & Guo, 2014). 2.2. Case definition The Taiwan Ministry of Health and Welfare registers all the cases of disability who are issued with a certificate by the local governments. Before a certificate can be issued, a patient needs to be confirmed as a case of SLD by a physician who was accredited by the government (Department of Health, 2006, 2008). According to the law, a case of SLD is defined as ‘‘Significant impairment in language comprehension, verbal expression, speech intelligibility, speech fluency, or vocal quality which interferes with communication.’’ Children with comorbidity of hearing impairment, intellectual disability, autism spectrum disorders, and multiple disabilities were excluded from the analyses (Department of Health, 2008). 2.3. Data collection The Department of Statistics of Taiwan Ministry of Health and Welfare publishes Statistical Yearbook each year (Ministry of Health and Welfare, 2014) (before the re-organiztion of the government in 2013, the reports were published by the Ministry of the Interior), and we analyzed the data from 2004 to 2010. The information includes the numbers of cases by age. Because the government discourages the certification under 3 years of age, we limited our analyses to those who were at least 3 years old (Department of Health, 2002).
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To assess the geographic differences, of the 25 areas (city or county) in Taiwan, we defined an ‘‘urban area’’ as one with more than 50% of the population living in metropolitan regions, which are defined by the Directorate-General of Budget, Accounting and Statistics of Taiwan (Ministry of the Interior, 2010a). Therefore, a ‘‘rural area’’ is one with 50% or less of the population living in metropolitan regions. Whereas data on the number of SLD cases between 3 and 17 years old by area and gender were not published in the yearbook, we obtained the information from the Department of Statistics of Ministry of the Interior, which is available since 2004 only. Moreover, because there was a re-organization of administration areas in 2011, we analyzed the data from 2004 to 2010. For calculating the prevalence, we also obtained the data from the Monthly Bulletin of Interior Statistics (Ministry of the Interior, 2010b), including the numbers of boys, girls, and total population in each age group in each area. 2.4. Data analysis We estimated prevalence by dividing the number of cases by the number of individuals in a specific group (3–5 year, 6–11 year, 12–14 year, and 15–17 year as categorized in the annual reports) in each year from 2004 to 2010 and evaluated the trend over the years (Table 1). Then, we estimated prevalence in boys and girls in each year by dividing the number of cases by the number of individuals in each gender also from 2004 to 2010 and obtained the prevalence rate ratio by dividing the prevalence rate in boys by the prevalence rate in girls in each year (Table 2). A 95% confidence interval was calculated for each rate ratio to evaluate its statistical significance. In addition, we calculated the boy-to-girl ratio by dividing the number of boy cases by the number of girl cases in each year. Likewise, we estimated prevalence in rural and urban areas in each year by dividing the number of cases by the number of individuals in each type of areas from 2004 to 2010 and obtained the prevalence rate ratio by dividing the prevalence rate in rural areas by the prevalence rate in urban areas in each year (Table 3). A 95% confidence interval was also calculated for each rate ratio to evaluate its statistical significance. We presented descriptive statistics of the variables as numbers or percentages and used linear regressions to evaluate the trends of changes in prevalence as well as gender and geographic differences. All the analyses were conducted using SAS 9.1, and all the statistical tests were performed at the two-tailed significance level of 0.05. This study was reviewed and approved by the Institution Review Board of the Ditmanson Medical Foundation Chia-Yi Christian Hospital. 3. Results From 2004 to 2010, the registered cases between 3 and 17 years old generally increased each year, from 1418 to 1637 (Table 1). The prevalence increased generally from 3.04/10,000 in 2004 to 4.05/10,000 in 2010 (p < 0.01). The prevalence rates in the age groups 3–5 years, 6–11 years, 12–14 years, and 15–17 years were 4.56–7.61/10,000, 3.69–5.36/10,000, 1.63– 2.16/10,000, and 1.66–2.07/10,000, respectively. The prevalence rates of all age groups generally increased over the years except for the age group 12–14 years (p < 0.01 for the age group 3–5 and 6–11 years, p = 0.057 for 15–17 years). Furthermore, the prevalence rates generally decreased with age in each year. From 2004 to 2010, there were more boy cases than girl cases in each year, and the boy-to-girl ratio ranged from 1.63 to 1.99 (mean = 1.79) (Table 2). The prevalence among boys ranged from 3.61/10,000 in 2004 to 5.17/10,000 in 2010. Rates among girls ranged from 2.42/10,000 in 2004 to 2.83/10,000 in 2010. The prevalence rates of boys and girls increased generally over the years (p < 0.01). The prevalence rate ratio ranged from 1.50 to 1.83 (p < 0.05 in all years), with an increasing trend over time (p < 0.01). Among the 7 cities and 18 counties in Taiwan, 7 cities and 5 counties were categorized as urban areas, and the remaining 13 counties were categorized as rural areas. From 2004 to 2010, rural areas had higher prevalence rates than urban areas. The prevalence among rural areas ranged from 3.72/10,000 in 2004 to 5.76/10,000 in 2010. Rates among urban areas ranged from 2.76/10,000 in 2004 to 3.36/10,000 in 2010. The prevalence rates of both rural and urban areas increased generally over the years (p < 0.01). The prevalence rate ratios of rural to urban areas ranged from 1.35 to 1.71 (p < 0.05 in all years), with an increasing trend over time (p < 0.01) (Table 3).
Table 1 The prevalence (per 10,000 children)a of speech and language disability by age in Taiwan. Year
2004 2005 2006 2007 2008 2009 2010 a
3–5 Year
6–11 Year
12–14 Year
15–17 Year
3–17 Year
N
(Pop)
Prev.
N
(Pop)
Prev.
N
(Pop)
Prev.
N
(Pop)
Prev.
N
(Pop)
Prev.
386 437 473 479 472 482 455
(846,130) (809,663) (730,819) (692,164) (654,179) (633,676) (621,318)
4.56 5.40 6.47 6.92 7.22 7.61 7.32
696 683 702 705 763 755 825
(1,887,027) (1,843,489) (1,826,824) (1,759,057) (1,682,797) (1,587,433) (1,538,830)
3.69 3.70 3.84 4.01 4.53 4.76 5.36
177 177 195 210 197 158 156
(973,188) (964,802) (968,634) (972,584) (968,553) (969,690) (912,829)
1.82 1.83 2.01 2.16 2.03 1.63 1.71
159 172 166 168 177 167 201
(957,965) (983,879) (961,550) (971,478) (963,101) (967,141) (971,456)
1.66 1.75 1.73 1.73 1.84 1.73 2.07
1418 1469 1536 1562 1609 1562 1637
(4,664,310) (4,601,833) (4,487,827) (4,395,283) (4,268,630) (4,157,940) (4,044,433)
3.04 3.19 3.42 3.55 3.77 3.76 4.05
The prevalence (Prev) was estimated by dividing N (number of cases) by Pop (population) in each age group in each year.
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Table 2 The prevalence and rate ratio by gender in children 3–17 years of age. Year
2004 2005 2006 2007 2008 2009 2010
Number of cases
Population
Prevalence (1/10,000)
Boy
Girl
Boy/girl
Boy
Girl
Boy
Girl
Rate ratio [95% CI]
878 916 960 1000 1047 1027 1089
540 553 576 562 562 535 548
1.63 1.66 1.67 1.78 1.86 1.92 1.99
2,429,513 2,397,970 2,339,532 2,292,296 2,225,403 2,167,065 2,107,777
2,234,797 2,203,863 2,148,295 2,102,987 2,043,227 1,990,875 1,936,656
3.61 3.82 4.10 4.36 4.70 4.74 5.17
2.42 2.51 2.68 2.67 2.75 2.69 2.83
1.50 1.52 1.53 1.63 1.71 1.76 1.83
[1.34,1.66]* [1.37,1.69]* [1.38,1.70]* [1.47,1.81]* [1.54,1.90]* [1.59,1.96]* [1.65,2.02]*
Boy/girl: boy-to-girl ratio, obtained by dividing the number of boy cases by the number of girl cases in each year; CI: confidence interval. * p < 0.05.
4. Discussion From 2004 to 2010, we found that the prevalence of SLD generally increased every year in all age groups in Taiwan except in 12–14 years of age. In each year there were more boy cases than girl cases, and a higher prevalence was observed in rural areas. Over the years, the boy-to-girl prevalence rate ratio increased from 1.50 to 1.83, with an increasing trend over time. Likewise, the rural-to-urban prevalence rate ratio increased from 1.35 to 1.71, also with an increasing trend over time. Many population-based studies reported prevalence of either speech disability or language disability alone, and the results varied widely. A nationwide study that applied a series of screening procedures found 10% to 13% of British 7-year-old children had an appreciable degree of speech impairment (Anonymous, 1973). A population-based survey of children aged 2–9 years in Jamaica found the prevalence of speech disability was 1.4% (Paul, Desai, & Thorburn, 1992). Data from the 1988 National Health Interview Survey in the United States showed that 1.89% of the children aged 0 through 17 years had stammering or stuttering, and 2.65% had other speech defects (Boyle, Decoufle´, & Yeargin-Allsopp, 1994). The Second National Sample Survey on Disability of China found that the prevalence of speech disability was 0.49% in children under 15 years of age (Zheng et al., 2008). In Iran-Yazd, a study of primary school students using direct and face to face assessment found a prevalence of speech disorders of 14.8% (Karbasi et al., 2011). The differences in age range, case definition, and casefinding method could all contribute to the variations across studies. As our study was on speech disability and language disability as a whole, the prevalence should be higher. However, because we used data on cases who were qualified for social benefits, the prevalence was lower than those observed in studies that included cases of severities at all levels. Some studies reported prevalence of speech disability and prevalence of language disability separately. It should be noted that comorbidity of speech disability and language disability is common. A study of a representative sample of 6-year-old children in the United States found a prevalence of 13.5% for language impairment and a prevalence of 3.8% for speech delay; with a 1.3% prevalence of comorbidity, the estimated prevalence of SLD was 16.0% (Shriberg, Tomblin, & McSweeny, 1999). A study of a representative sample of 5-year-old kindergarten children in the Ottawa-Carleton region in Canada estimated that between 16.2% and 21.8% of the total reference population had SLD, but the prevalence of comorbidity was much higher: 64% of boys and 70% of girls who had speech problems also had language impairment (Beitchman et al., 1986). In a study in northern Tasmania, Australia, of the 127 preparatory students with SLD, 27 (21.3%) had isolated speech impairment, 56 (44.1%) had isolated language impairment, and 44 (34.6%) had comorbid speech and language impairment (Jessup, Ward, Cahill, & Keating, 2008). Shriberg et al. (1999) conducted a review of literature and found that the reported prevalence of the comorbidity ranged widely, from 11% to 77% with speech disorders as the index and from 9% to 75% with language disorders as the index. In our study, speech disability and language disability were assessed as a whole, and therefore each case was counted only once in each year. Most large scale population-based studies on SLD are on specific disorders, and those on SLD in general are limited. Even though almost all large scale population-based studies on SLD in general were conducted in Western countries, the Table 3 The prevalence and rate ratio by geographic area in children 3–17 years of age. Year
2004 2005 2006 2007 2008 2009 2010
Number of cases
Population
Prevalence (1/10,000)
Rural
Urban
Rural
Urban
Rural
Urban
Rate ratio [95% CI]
507 530 588 593 636 632 665
911 939 948 969 973 930 972
1,363,979 1,339,995 1,302,738 1,270,284 1,229,992 1,195,230 1,154,481
3,300,331 3,261,838 3,185,089 3,124,999 3,038,638 2,962,710 2,889,952
3.72 3.96 4.51 4.67 5.17 5.29 5.76
2.76 2.88 2.98 3.10 3.20 3.14 3.36
1.35 1.37 1.52 1.51 1.61 1.68 1.71
CI: confidence interval. * p < 0.05.
[1.21,1.50]* [1.24,1.53]* [1.37,1.68]* [1.36,1.67]* [1.46,1.78]* [1.52,1.86]* [1.55,1.89]*
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Table 4 Population-based studies on the prevalence of unspecified speech and language disability (impairment). Study (study period)
Country (area)
Participants
Age (year)
Prevalence (%) Outcome
Measurement
Bax, Hart, and Jenkins (1983) (1974–1975) Beitchman et al. (1986) (1982) Shriberg et al. (1999) (unspecified) Glascoe (2001) (unspecified) McLeod and Harrison (2009) (unspecified)
UK (London)
269 323 269 1655
2 3 4.5 5
5 8 5 10.9
Definite abnormal speech and language
Pesonal interview and examination Assessment by SLPa
1328
6
16.0
Some speech and language impairment Speech and language delay
5.5
Speech–language impaired
a b
Canada (Ottawa–Carleton) USA USA Australia
512 4983
7/12–8 4–5
14.5
Speech and language impairment requiring services of SLP
Analysis of audio-recording using a computer program Performance 2 standard deviation below the meanb Received services of SLP in the last 12 months
Speech–language pathologist. On language measures or Child Developmental Inventory subsets of expressive and receptive language.
reported prevalence still varied widely (Table 4). The differences in age range, case definition, and case-finding method make the comparison of prevalence among studies very difficult. When comparing with studies of SLD in Western countries, we believe the prevalence in our study was underestimated, because we adopted the data from a national registry to generate ‘‘administrative’’ prevalence, and such a method generally observes lower prevalence rates as it tends to identify only persons who are receiving services provided by the administration (Larson et al., 2001). In addition, some other developmental disabilities such as hearing impairment, intellectual disabilities, cerebral palsy, and autism spectrum disorders are common risk factors for SLD, but cases with comorbidity of those conditions were excluded from our analyses due to the classification system applied by the registry. In fact, the disability registry in Taiwan categorizes SLD cases concurrent with other disabilities as cases of ‘‘multiple disabilities’’ instead of SLD (Department of Health, 2008), and this could also underestimate the number of cases. For example, the Second National Sample Survey on Disability of the Mainland China showed the 23.94% of the children with speech disability under 15 years of age had hearing loss, and 10.33% had low IQ; only 29.43% had no other identifiable disorders (Zheng et al., 2008). We found that the age group 3–5 years had the highest prevalence rate of SLD, and this is compatible with the data from the 1995 Australian Health Survey, in which the peak prevalence of speech disorders occurred at age 5 in boys and at age 3 to 4 in girls (Keating, Turrell, & Ozanne, 2001). Similar decreasing trends with age were also observed in a study on a representative sample of the Dutch population (Spee-van der Wekke, den Ouden, Meulmeester, & Radder, 2000) and the Second National Sample Survey on Disability of China (Zheng et al., 2008). However, using the same registry, we found that some other developmental disabilities, including intellectual disabilities (Lai et al., 2012b) and hearing impairment (Lai et al., 2014), increased with age in childhood. We believe the main reasons are that most cases of those developmental disabilities are rarely fatal and that a large proportion of cases are not curable. While SLD cases are also rarely fatal in childhood, in contrast, substantial improvement can be achieved in many cases. We believe that a substantial proportion of the decrease after 6 years of age in Taiwan was attributable to the improvement achieved by school education because primary school education (between 6 and 11 years old in most cases) and junior high school education (between 12 and 14 years old in most cases) are compulsory in Taiwan. In addition, a prospective study suggested that approximately 75% of children with speech delay normalized by 6 years of age (Shriberg et al., 1999), and another study argued that speech disabilities are subject to maturation and tend to dissolve with increasing age (Spee-van der Wekke et al., 2000). The increasing trend of SLD prevalence over time in the study period was similar to the trends found in some other developmental disabilities in the same registry, including intellectual disabilities and autism spectrum disorders (Lai et al., 2012a, 2013). In a previous study, we found that from 2000 to 2011, the overall (both genders combined) prevalence of SLD had a constant increasing trend (p < 0.01 for the trend test) (Lai et al., 2013), and in this study, we observed an increasing trend in both boys and girls. We believe the increase is unlikely to be a true increase in the occurrence of cases, because many of the risk factors such as levels of parental education, larger family size, and poor maternal well-being (Harrison & McLeod, 2010; US Preventive Services Task Force, 2006) had moved toward the favorable direction, or at least remained similar, in Taiwan. Whereas some other developmental disabilities such as hearing impairment, intellectual disabilities, cerebral palsy, and autism spectrum disorders are risk factors for SLD, cases with comorbidity of those conditions have been excluded from the analyses. Therefore, the increase is more likely to be attributable to an increase in the proportion of cases registered. This phenomenon may be in turn attributable to higher awareness in parents and professionals (Matson & Kozlowski, 2011), better service of the agencies (Yeargin-Allsopp, Murphy, Oakley, & Sikes, 1992), more willingness to register, etc. (Lai et al., 2011). Male gender is a risk factor of SLD (Spee-van der Wekke et al., 2000; US Preventive Services Task Force, 2006; Harrison & McLeod, 2010), and more than two decades ago, a study of a national sample of 9854 Israeli Jewish children aged 2 to 3 years who were born in 1980 had found that speech and language disorders were more prevalent among male children (Bendel, Palti, Winter, & Ornoy, 1989). In Taiwan, we observed rate ratios between 1.50 and 1.83, and the range is compatible with the
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ratio observed in the Second National Sample Survey on Disability of the Mainland China—0.61% vs. 0.46% (Zheng et al., 2008). Likewise, a study report on a demographically representative population sample of 7218 children 6 years of age in the United States showed that the prevalence of speech delay was approximately 1.5 times more prevalent in boys (4.5% vs. 3.1%) and that of language impairment was also more prevalent in boys (14.2% vs. 11.9%) (Shriberg et al., 1999). A literature review conducted by the authors of that report found that the male-to-female rate ratios of moderate to severe speech delay of unknown origin ranged from 1.5 to 2.4 in five studies on children 5 to 8 years of age. With a wider age range, data from the 1995 Australian Health Survey on children aged 0–14 years also showed that boys had a higher prevalence of speech disorders (Keating et al., 2001). Furthermore, a study on 13,182 school beginners in Bavaria, Germany found boys had higher prevalence for all three types of speech impairments: 17.8% vs. 9.5% for pronunciation, 5.1% vs. 2.8% for grammar, and 4.1% vs. 2.0% for rhythm of speech (Stich, Baune, Caniato, Mikolajczyk, & Kra¨mer, 2012). While it is well documented that more boys than girls have SLD, the underlying mechanisms are unclear. In general, boys lag girls in speech and language development, and the Dunedin studies (Silva, 1987) found that the girls began to talk a month earlier than the boys on average and that they gained significantly higher scores on all the language tests. Bias in ascertainment has also been noted, as boys usually receive greater attention, are charged with higher family expectations, and have more behavior problems than girls, and therefore they are more likely to be referred for services and be reported (Shriberg et al., 1999). However, as gender equality has been improving over the years in Taiwan, such an ascertainment bias should decrease over time and lead to a decreasing trend in the boy-to-girl prevalence ratio, instead of an increasing tread as observed in our study. Further study identifying the risk factors that contributed to the increasing trend may help the prevention of SLD in the future. From 2004 to 2010, the prevalence rates of SLD were higher in rural areas in Taiwan, and the rate ratios ranged from 1.35 to 1.71. The findings are compatible with those of the Second National Sample Survey on Disability of China, in which the ratio was 1.52 (0.60% vs. 0.40%) (Zheng et al., 2008). However, a study on a demographically representative population sample of 6-year-old children in the United States observed a positive association between urbanization and the prevalence of speech delay: 4.9% in urban areas, 3.7% in suburban areas, and 2.3% in rural areas (Shriberg et al., 1999). We speculate that in less developed countries where maternal health and childhood education play important roles in the etiology of SLD, the prevalence of SLD has a negative association with urbanization, but in far developed countries where diagnosis and reporting are important factors affecting the prevalence, the association becomes positive. For example, the 1995 Australian Health Survey on children aged 0–14 years found no relationship between socioeconomic status and childhood speech disorders (Keating et al., 2001), but studies in the developing countries frequently observed a negative association (Hamdan & Al-Akhras, 2009; Zheng et al., 2008). Such international comparisons may help identifying the risk factors for SLD and cast some light on the prevention strategy. The major limitation of our study is that we used ‘‘administrative prevalence’’ data, which do not include persons who did not receive services provided by the administration. Moreover, we did not have incidence data, and this limits the identification of risk factors (Lai et al., 2011). In addition, patients with less serious disabilities that did not meet the certification criteria were not included in our analyses. In fact, with one-by-one screening and tests, a study of 410 children 5 to 6 years old sampled from two municipals of Taiwan identified 22 as having developmental speech and language disorders, yielding a prevalence rate of 6.1% (Cheng, Chen, Tsai, Chen, & Cherng, 2009), which is closer to the prevalence reported in other developed countries. Therefore, our results can be generalized to severe cases of SLD only. Furthermore, the government does not release the individual data, which makes it impossible to explore related issues in greater details. Nonetheless, in comparison with previous studies, the current study has some unique features. First of all, this study provides data at the national level. Besides the large number of cases (1637 cases in 2010 alone for example) that can offer stable statistical estimates, it can facilitate unbiased international comparisons, which is important in identifying the risk factors and constructing prevention strategies. In addition, all the cases were closely observed and then certified by physicians, making the diagnosis reliable. Furthermore, the duration of data collection lasted for 7 years, not just one as in most large-scale studies, and this allowed us to assess the time trend, which is rarely assessed in the previous studies. 5. Conclusions While a previous study found that the overall (both genders combined) prevalence of SLD in Taiwan had a constant increasing trend from 2000 to 2011, in this study, we found that the prevalence of SLD in Taiwan generally increased from 2004 to 2010 in all age groups, with the age group 3–5 years having the highest prevalence rate. Like studies in most countries in the world, the prevalence rates are higher in boys than in girls, and the rate ratio had an increasing trend over time. Further study identifying the risk factors that contributed to the differences between the two genders may help the prevention of SLD in the future. The prevalence rates are higher in rural areas than in urban areas, which is similar to many studies in developing countries but not consistent with most studies in developed countries. Likewise, the prevalence rate ratio of rural areas to urban areas had an increasing trend over time. Further international comparisons may help identifying the risk factors for SLD and cast some light on the prevention strategy. Whereas our study has provided data at the national level, which are rarely available, further analyses of the individual data are desirable.
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Acknowledgments We would like to thank Department of Statistics of Ministry of the Interior for providing the registry data and Mr. ChengHsing Yeh at the Ditmanson Medical Foundation Chia-Yi Christian Hospital for his assistance in statistical analysis.
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Journal of Speech Language, and Hearing Research, 52, 1213–1229. Ministry of the Interior (2010a). Monthly bulletin of interior statistics: 01-07 population for township and district and by urban area. Taipei, Taiwan: Department of Statistics, Ministry of the Interior http://sowf.moi.gov.tw/stat/month/elist.htm. Accessed 07.10.14. Ministry of the Interior (2010b). Monthly bulletin of interior statistics: 01-11 population by single year of age. Taipei, Taiwan: Department of Statistics, Ministry of the Interior http://sowf.moi.gov.tw/stat/month/elist.htm. Accessed 07.10.14. Ministry of Health Welfare (2014). Statistical yearbook of welfare: 6-4 the disabled population by classification and age. Taipei, Taiwan: Department of Statistics, Ministry of Health and Welfare http://www.mohw.gov.tw/cht/DOS/Statistic.aspx?f_list_no=312&fod_list_no=4182. Accessed 07.10.14. Paul, T. J., Desai, P., & Thorburn, M. J. (1992). The prevalence of childhood disability and related medical diagnoses in Clarendon, Jamaica. West Indian Medical Journal, 41, 8–11. Physically and Mentally Disabled Citizens Protection Act (2001). Revision in 2001, President Order Hua-Tzon (1) Yi-Tze No. 9000224680. 21 November 2001. Shriberg, L. D., Tomblin, J. B., & McSweeny, J. L. (1999). Prevalence of speech delay in 6-year-old children and comorbidity with language impairment. Journal of Speech Language, and Hearing Research, 42, 1461–1481. Silva, P. A. (1987). Epidemiology, longitudinal course and some associated factors: An update. In W. Yule & M. Rutter (Eds.), Language development and disorders (pp. 1–15). Oxford: Blackwell Scientific. Spee-van der Wekke, J., den Ouden, A. L., Meulmeester, J. F., & Radder, J. J. (2000). Self-reported physical disabilities in children in the Netherlands. Disability & Rehabilitation, 22, 323–329. Stich, H. L., Baune, B. T., Caniato, R. N., Mikolajczyk, R. T., & Kra¨mer, A. (2012). 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Contents lists available at ScienceDirect
Research in Developmental Disabilities
Gender and geographic differences in the prevalence of reportable childhood speech and language disability in Taiwan Yen-Cheng Tseng a, Der-Chung Lai b,c, How-Ran Guo d,e,* a
Department of Business Administration and Language Education Center, Chang Jung Christian University, Tainan, Taiwan Department of Physical Medicine and Rehabilitation, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Chia-Yi, Taiwan Department of Senior Citizen Service Management, Chia Nan University of Pharmacy & Science, Tainan, Taiwan d Department of Environmental and Occupational Health, National Cheng Kung University, Tainan, Taiwan e Department of Occupational and Environmental Medicine, National Cheng Kung University Hospital, Tainan, Taiwan b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 13 October 2014 Received in revised form 5 January 2015 Accepted 28 January 2015 Available online
Speech and language disability (SLD) is not uncommon in children. However, data at the national level are limited, and geographic differences are seldom evaluated. Starting from 1980, the local governments in Taiwan has begun to certify disabled residents for providing various services and report cases to the central government according to the law, and the central government maintains a registry of reported cases, which provides a unique opportunity for studying SLD at the national level. Using the registry data from 2004 to 2010, we calculated the prevalence of SLD by age, gender, and geographic area and assessed the changes over time. Because the government discourages the certification under 3 years of age, we excluded cases under 3 years old from the analyses. We found that from 2004 to 2010 the registered cases between 3 and 17 years old increased from 1418 to 1637 per year, and the prevalence generally increased every year in all age groups except in 12–14 years of age. In each year there were more boy cases than girl cases, and the prevalence rate ratio increased from 1.50 to 1.83 (p < 0.05 in all years), with an increasing trend over time (p < 0.01). A higher prevalence was observed in the rural areas over the years, and the prevalence rate ratio increased from 1.35 to 1.71 (p < 0.05 in all years), with an increasing trend over time (p < 0.01). Further studies identifying the risk factors contributed to the increases might help the prevention of SLD in the future. ß 2015 Elsevier Ltd. All rights reserved.
Keywords: Speech and language disability Impairment Prevalence Registry Gender Geographic distribution Taiwan
1. Introduction Speech and language disability (SLD) is a cluster of developmental disorders that may affect a person’s ability in communication, which is important in school performance, career development, and daily social life. According to the American Speech–Language-Hearing Association (2014), a speech disorder is characterized by having problems with voice or the inability to produce speech sounds correctly or fluently, and a language disorder is characterized by having trouble understanding others or sharing thoughts, ideas, and feelings completely. SLD can be developed in both children and
* Corresponding author at: Department of Environmental and Occupational Health, National Cheng Kung University, 138 Sheng-Li Road, Tainan 70428, Taiwan. Tel.: +886 6 2353535/5802; fax: +886 6 2752484. E-mail address: [email protected] (H.-R. Guo). http://dx.doi.org/10.1016/j.ridd.2015.01.009 0891-4222/ß 2015 Elsevier Ltd. All rights reserved.
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adults, but the reported prevalence ranges widely. For example, the Second National Sample Survey on Disability of China on 2,526,145 individuals found the prevalence of speech disability was 0.53% in 2006 (Zheng, Zhang, Chen, Pei, & Song, 2008), but a house-to-house survey of 10,147 families in rural communities in the north of the West Bank found the prevalence of speech disability was as high as 11.4% around the same time (Hamdan & Al-Akhras, 2009). In the United States, it was estimated that 5% to 8% of preschool children were affected by speech and language delay (US Preventive Services Task Force, 2006). In addition to differences in the incidence of SLD, the large variation in the reported prevalence across studies may be attributable to differences in the case definition, age range, and case finding method (Durkin, 2002; Karbasi, Fallah, & Golestan, 2011). When developed in the childhood, SLD has a larger impact and may persist into later life (American Speech–LanguageHearing Association, 2014; Glogowska, Roulstone, Peters, & Enderby, 2006; US Preventive Services Task Force, 2006), and therefore it is a great concern of parents. For example, in a study of Australian children aged 4–5 years, 25.2% of the parents had concerns about the expressive language ability of their children and 9.5% had concerns about their receptive language ability, which led to accessing speech–language pathologist (SLP) services in 14.5% of the children (McLeod & Harrison, 2009). SLD is not uncommon in children, but geographic differences in terms of urbanization are seldom evaluated. Even though the number of related studies is limited, the results are inconsistent. While a survey of 10,147 rural families in the West Bank found a high prevalence of speech disability as 11.4% (Hamdan & Al-Akhras, 2009), a survey of 25,196 rural families in Pakistan found the prevalence of speech delay was only 0.047% (Ibrahim & Bhutta, 2013). A study compared 100 children 1–60 months old each from two suburban and one urban communities of Mexico and found the prevalence of language failure was higher in one of the suburban community (22%), while the other two had the same prevalence of 13% (Guadarrama-Celaya et al., 2012). However, the number of participants was small, and the difference did not reach statistical significance. According to the Disabled Welfare Law (1980), the local governments in Taiwan certify the disabled residents and provide various services, and the Ministry of Health and Welfare maintains a registry of reported cases. The Department of Statistics of Ministry of Health and Welfare (2014) publishes summary data each year and the registry data of Taiwan present a rare opportunity for studying the epidemiology of SLD at the national level. In a previous study, we analyzed the data and found a constant increasing trend in the prevalence of SLD from 2000 to 2011 (Lai, Tseng, & Guo, 2013), but we did not compare SLD between the two genders or evaluate the geographic difference. Therefore, we used the data from 2004 to 2010 to assess the changes in prevalence, gender, and geographic differences of SLD in Taiwanese children over time. 2. Methods 2.1. The disability registry system in Taiwan The promulgation of the Disabled Welfare Law in 1980 is a milestone in the history of promoting disability registry in Taiwan. The categorization system covered seven types of disabilities (SLD, visual impairment, hearing impairment or balance disability, disability of limbs, intellectual disability, multiple disabilities, and other disabilities listed by the Department of Health) initially (Disabled Welfare Act, 1980), and nine other types were added from 1981 to 2001 (Physically and Mentally Disabled Citizens Protection Act, 2001). ‘‘Multiple disabilities’’ means the concurrence of two or more disabilities (Department of Health, 2008). According to the law, the local governments began to certify disabled residents and provide various services in 1980, and patients with disabilities can make applications for certification through the local government office in their residential areas. The local governments report cases to the central government, and the Ministry of Health and Welfare maintains a registry of reported cases. We have adopted the registry data to conduct a series of studies on developmental disabilities (Lai, Tseng, & Guo, 2011; Lai, Tseng, Hou, & Guo, 2012a, 2012b; Lai et al., 2013; Lai, Tseng, Lin, & Guo, 2014). 2.2. Case definition The Taiwan Ministry of Health and Welfare registers all the cases of disability who are issued with a certificate by the local governments. Before a certificate can be issued, a patient needs to be confirmed as a case of SLD by a physician who was accredited by the government (Department of Health, 2006, 2008). According to the law, a case of SLD is defined as ‘‘Significant impairment in language comprehension, verbal expression, speech intelligibility, speech fluency, or vocal quality which interferes with communication.’’ Children with comorbidity of hearing impairment, intellectual disability, autism spectrum disorders, and multiple disabilities were excluded from the analyses (Department of Health, 2008). 2.3. Data collection The Department of Statistics of Taiwan Ministry of Health and Welfare publishes Statistical Yearbook each year (Ministry of Health and Welfare, 2014) (before the re-organiztion of the government in 2013, the reports were published by the Ministry of the Interior), and we analyzed the data from 2004 to 2010. The information includes the numbers of cases by age. Because the government discourages the certification under 3 years of age, we limited our analyses to those who were at least 3 years old (Department of Health, 2002).
Y.-C. Tseng et al. / Research in Developmental Disabilities 40 (2015) 11–18
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To assess the geographic differences, of the 25 areas (city or county) in Taiwan, we defined an ‘‘urban area’’ as one with more than 50% of the population living in metropolitan regions, which are defined by the Directorate-General of Budget, Accounting and Statistics of Taiwan (Ministry of the Interior, 2010a). Therefore, a ‘‘rural area’’ is one with 50% or less of the population living in metropolitan regions. Whereas data on the number of SLD cases between 3 and 17 years old by area and gender were not published in the yearbook, we obtained the information from the Department of Statistics of Ministry of the Interior, which is available since 2004 only. Moreover, because there was a re-organization of administration areas in 2011, we analyzed the data from 2004 to 2010. For calculating the prevalence, we also obtained the data from the Monthly Bulletin of Interior Statistics (Ministry of the Interior, 2010b), including the numbers of boys, girls, and total population in each age group in each area. 2.4. Data analysis We estimated prevalence by dividing the number of cases by the number of individuals in a specific group (3–5 year, 6–11 year, 12–14 year, and 15–17 year as categorized in the annual reports) in each year from 2004 to 2010 and evaluated the trend over the years (Table 1). Then, we estimated prevalence in boys and girls in each year by dividing the number of cases by the number of individuals in each gender also from 2004 to 2010 and obtained the prevalence rate ratio by dividing the prevalence rate in boys by the prevalence rate in girls in each year (Table 2). A 95% confidence interval was calculated for each rate ratio to evaluate its statistical significance. In addition, we calculated the boy-to-girl ratio by dividing the number of boy cases by the number of girl cases in each year. Likewise, we estimated prevalence in rural and urban areas in each year by dividing the number of cases by the number of individuals in each type of areas from 2004 to 2010 and obtained the prevalence rate ratio by dividing the prevalence rate in rural areas by the prevalence rate in urban areas in each year (Table 3). A 95% confidence interval was also calculated for each rate ratio to evaluate its statistical significance. We presented descriptive statistics of the variables as numbers or percentages and used linear regressions to evaluate the trends of changes in prevalence as well as gender and geographic differences. All the analyses were conducted using SAS 9.1, and all the statistical tests were performed at the two-tailed significance level of 0.05. This study was reviewed and approved by the Institution Review Board of the Ditmanson Medical Foundation Chia-Yi Christian Hospital. 3. Results From 2004 to 2010, the registered cases between 3 and 17 years old generally increased each year, from 1418 to 1637 (Table 1). The prevalence increased generally from 3.04/10,000 in 2004 to 4.05/10,000 in 2010 (p < 0.01). The prevalence rates in the age groups 3–5 years, 6–11 years, 12–14 years, and 15–17 years were 4.56–7.61/10,000, 3.69–5.36/10,000, 1.63– 2.16/10,000, and 1.66–2.07/10,000, respectively. The prevalence rates of all age groups generally increased over the years except for the age group 12–14 years (p < 0.01 for the age group 3–5 and 6–11 years, p = 0.057 for 15–17 years). Furthermore, the prevalence rates generally decreased with age in each year. From 2004 to 2010, there were more boy cases than girl cases in each year, and the boy-to-girl ratio ranged from 1.63 to 1.99 (mean = 1.79) (Table 2). The prevalence among boys ranged from 3.61/10,000 in 2004 to 5.17/10,000 in 2010. Rates among girls ranged from 2.42/10,000 in 2004 to 2.83/10,000 in 2010. The prevalence rates of boys and girls increased generally over the years (p < 0.01). The prevalence rate ratio ranged from 1.50 to 1.83 (p < 0.05 in all years), with an increasing trend over time (p < 0.01). Among the 7 cities and 18 counties in Taiwan, 7 cities and 5 counties were categorized as urban areas, and the remaining 13 counties were categorized as rural areas. From 2004 to 2010, rural areas had higher prevalence rates than urban areas. The prevalence among rural areas ranged from 3.72/10,000 in 2004 to 5.76/10,000 in 2010. Rates among urban areas ranged from 2.76/10,000 in 2004 to 3.36/10,000 in 2010. The prevalence rates of both rural and urban areas increased generally over the years (p < 0.01). The prevalence rate ratios of rural to urban areas ranged from 1.35 to 1.71 (p < 0.05 in all years), with an increasing trend over time (p < 0.01) (Table 3).
Table 1 The prevalence (per 10,000 children)a of speech and language disability by age in Taiwan. Year
2004 2005 2006 2007 2008 2009 2010 a
3–5 Year
6–11 Year
12–14 Year
15–17 Year
3–17 Year
N
(Pop)
Prev.
N
(Pop)
Prev.
N
(Pop)
Prev.
N
(Pop)
Prev.
N
(Pop)
Prev.
386 437 473 479 472 482 455
(846,130) (809,663) (730,819) (692,164) (654,179) (633,676) (621,318)
4.56 5.40 6.47 6.92 7.22 7.61 7.32
696 683 702 705 763 755 825
(1,887,027) (1,843,489) (1,826,824) (1,759,057) (1,682,797) (1,587,433) (1,538,830)
3.69 3.70 3.84 4.01 4.53 4.76 5.36
177 177 195 210 197 158 156
(973,188) (964,802) (968,634) (972,584) (968,553) (969,690) (912,829)
1.82 1.83 2.01 2.16 2.03 1.63 1.71
159 172 166 168 177 167 201
(957,965) (983,879) (961,550) (971,478) (963,101) (967,141) (971,456)
1.66 1.75 1.73 1.73 1.84 1.73 2.07
1418 1469 1536 1562 1609 1562 1637
(4,664,310) (4,601,833) (4,487,827) (4,395,283) (4,268,630) (4,157,940) (4,044,433)
3.04 3.19 3.42 3.55 3.77 3.76 4.05
The prevalence (Prev) was estimated by dividing N (number of cases) by Pop (population) in each age group in each year.
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Table 2 The prevalence and rate ratio by gender in children 3–17 years of age. Year
2004 2005 2006 2007 2008 2009 2010
Number of cases
Population
Prevalence (1/10,000)
Boy
Girl
Boy/girl
Boy
Girl
Boy
Girl
Rate ratio [95% CI]
878 916 960 1000 1047 1027 1089
540 553 576 562 562 535 548
1.63 1.66 1.67 1.78 1.86 1.92 1.99
2,429,513 2,397,970 2,339,532 2,292,296 2,225,403 2,167,065 2,107,777
2,234,797 2,203,863 2,148,295 2,102,987 2,043,227 1,990,875 1,936,656
3.61 3.82 4.10 4.36 4.70 4.74 5.17
2.42 2.51 2.68 2.67 2.75 2.69 2.83
1.50 1.52 1.53 1.63 1.71 1.76 1.83
[1.34,1.66]* [1.37,1.69]* [1.38,1.70]* [1.47,1.81]* [1.54,1.90]* [1.59,1.96]* [1.65,2.02]*
Boy/girl: boy-to-girl ratio, obtained by dividing the number of boy cases by the number of girl cases in each year; CI: confidence interval. * p < 0.05.
4. Discussion From 2004 to 2010, we found that the prevalence of SLD generally increased every year in all age groups in Taiwan except in 12–14 years of age. In each year there were more boy cases than girl cases, and a higher prevalence was observed in rural areas. Over the years, the boy-to-girl prevalence rate ratio increased from 1.50 to 1.83, with an increasing trend over time. Likewise, the rural-to-urban prevalence rate ratio increased from 1.35 to 1.71, also with an increasing trend over time. Many population-based studies reported prevalence of either speech disability or language disability alone, and the results varied widely. A nationwide study that applied a series of screening procedures found 10% to 13% of British 7-year-old children had an appreciable degree of speech impairment (Anonymous, 1973). A population-based survey of children aged 2–9 years in Jamaica found the prevalence of speech disability was 1.4% (Paul, Desai, & Thorburn, 1992). Data from the 1988 National Health Interview Survey in the United States showed that 1.89% of the children aged 0 through 17 years had stammering or stuttering, and 2.65% had other speech defects (Boyle, Decoufle´, & Yeargin-Allsopp, 1994). The Second National Sample Survey on Disability of China found that the prevalence of speech disability was 0.49% in children under 15 years of age (Zheng et al., 2008). In Iran-Yazd, a study of primary school students using direct and face to face assessment found a prevalence of speech disorders of 14.8% (Karbasi et al., 2011). The differences in age range, case definition, and casefinding method could all contribute to the variations across studies. As our study was on speech disability and language disability as a whole, the prevalence should be higher. However, because we used data on cases who were qualified for social benefits, the prevalence was lower than those observed in studies that included cases of severities at all levels. Some studies reported prevalence of speech disability and prevalence of language disability separately. It should be noted that comorbidity of speech disability and language disability is common. A study of a representative sample of 6-year-old children in the United States found a prevalence of 13.5% for language impairment and a prevalence of 3.8% for speech delay; with a 1.3% prevalence of comorbidity, the estimated prevalence of SLD was 16.0% (Shriberg, Tomblin, & McSweeny, 1999). A study of a representative sample of 5-year-old kindergarten children in the Ottawa-Carleton region in Canada estimated that between 16.2% and 21.8% of the total reference population had SLD, but the prevalence of comorbidity was much higher: 64% of boys and 70% of girls who had speech problems also had language impairment (Beitchman et al., 1986). In a study in northern Tasmania, Australia, of the 127 preparatory students with SLD, 27 (21.3%) had isolated speech impairment, 56 (44.1%) had isolated language impairment, and 44 (34.6%) had comorbid speech and language impairment (Jessup, Ward, Cahill, & Keating, 2008). Shriberg et al. (1999) conducted a review of literature and found that the reported prevalence of the comorbidity ranged widely, from 11% to 77% with speech disorders as the index and from 9% to 75% with language disorders as the index. In our study, speech disability and language disability were assessed as a whole, and therefore each case was counted only once in each year. Most large scale population-based studies on SLD are on specific disorders, and those on SLD in general are limited. Even though almost all large scale population-based studies on SLD in general were conducted in Western countries, the Table 3 The prevalence and rate ratio by geographic area in children 3–17 years of age. Year
2004 2005 2006 2007 2008 2009 2010
Number of cases
Population
Prevalence (1/10,000)
Rural
Urban
Rural
Urban
Rural
Urban
Rate ratio [95% CI]
507 530 588 593 636 632 665
911 939 948 969 973 930 972
1,363,979 1,339,995 1,302,738 1,270,284 1,229,992 1,195,230 1,154,481
3,300,331 3,261,838 3,185,089 3,124,999 3,038,638 2,962,710 2,889,952
3.72 3.96 4.51 4.67 5.17 5.29 5.76
2.76 2.88 2.98 3.10 3.20 3.14 3.36
1.35 1.37 1.52 1.51 1.61 1.68 1.71
CI: confidence interval. * p < 0.05.
[1.21,1.50]* [1.24,1.53]* [1.37,1.68]* [1.36,1.67]* [1.46,1.78]* [1.52,1.86]* [1.55,1.89]*
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Table 4 Population-based studies on the prevalence of unspecified speech and language disability (impairment). Study (study period)
Country (area)
Participants
Age (year)
Prevalence (%) Outcome
Measurement
Bax, Hart, and Jenkins (1983) (1974–1975) Beitchman et al. (1986) (1982) Shriberg et al. (1999) (unspecified) Glascoe (2001) (unspecified) McLeod and Harrison (2009) (unspecified)
UK (London)
269 323 269 1655
2 3 4.5 5
5 8 5 10.9
Definite abnormal speech and language
Pesonal interview and examination Assessment by SLPa
1328
6
16.0
Some speech and language impairment Speech and language delay
5.5
Speech–language impaired
a b
Canada (Ottawa–Carleton) USA USA Australia
512 4983
7/12–8 4–5
14.5
Speech and language impairment requiring services of SLP
Analysis of audio-recording using a computer program Performance 2 standard deviation below the meanb Received services of SLP in the last 12 months
Speech–language pathologist. On language measures or Child Developmental Inventory subsets of expressive and receptive language.
reported prevalence still varied widely (Table 4). The differences in age range, case definition, and case-finding method make the comparison of prevalence among studies very difficult. When comparing with studies of SLD in Western countries, we believe the prevalence in our study was underestimated, because we adopted the data from a national registry to generate ‘‘administrative’’ prevalence, and such a method generally observes lower prevalence rates as it tends to identify only persons who are receiving services provided by the administration (Larson et al., 2001). In addition, some other developmental disabilities such as hearing impairment, intellectual disabilities, cerebral palsy, and autism spectrum disorders are common risk factors for SLD, but cases with comorbidity of those conditions were excluded from our analyses due to the classification system applied by the registry. In fact, the disability registry in Taiwan categorizes SLD cases concurrent with other disabilities as cases of ‘‘multiple disabilities’’ instead of SLD (Department of Health, 2008), and this could also underestimate the number of cases. For example, the Second National Sample Survey on Disability of the Mainland China showed the 23.94% of the children with speech disability under 15 years of age had hearing loss, and 10.33% had low IQ; only 29.43% had no other identifiable disorders (Zheng et al., 2008). We found that the age group 3–5 years had the highest prevalence rate of SLD, and this is compatible with the data from the 1995 Australian Health Survey, in which the peak prevalence of speech disorders occurred at age 5 in boys and at age 3 to 4 in girls (Keating, Turrell, & Ozanne, 2001). Similar decreasing trends with age were also observed in a study on a representative sample of the Dutch population (Spee-van der Wekke, den Ouden, Meulmeester, & Radder, 2000) and the Second National Sample Survey on Disability of China (Zheng et al., 2008). However, using the same registry, we found that some other developmental disabilities, including intellectual disabilities (Lai et al., 2012b) and hearing impairment (Lai et al., 2014), increased with age in childhood. We believe the main reasons are that most cases of those developmental disabilities are rarely fatal and that a large proportion of cases are not curable. While SLD cases are also rarely fatal in childhood, in contrast, substantial improvement can be achieved in many cases. We believe that a substantial proportion of the decrease after 6 years of age in Taiwan was attributable to the improvement achieved by school education because primary school education (between 6 and 11 years old in most cases) and junior high school education (between 12 and 14 years old in most cases) are compulsory in Taiwan. In addition, a prospective study suggested that approximately 75% of children with speech delay normalized by 6 years of age (Shriberg et al., 1999), and another study argued that speech disabilities are subject to maturation and tend to dissolve with increasing age (Spee-van der Wekke et al., 2000). The increasing trend of SLD prevalence over time in the study period was similar to the trends found in some other developmental disabilities in the same registry, including intellectual disabilities and autism spectrum disorders (Lai et al., 2012a, 2013). In a previous study, we found that from 2000 to 2011, the overall (both genders combined) prevalence of SLD had a constant increasing trend (p < 0.01 for the trend test) (Lai et al., 2013), and in this study, we observed an increasing trend in both boys and girls. We believe the increase is unlikely to be a true increase in the occurrence of cases, because many of the risk factors such as levels of parental education, larger family size, and poor maternal well-being (Harrison & McLeod, 2010; US Preventive Services Task Force, 2006) had moved toward the favorable direction, or at least remained similar, in Taiwan. Whereas some other developmental disabilities such as hearing impairment, intellectual disabilities, cerebral palsy, and autism spectrum disorders are risk factors for SLD, cases with comorbidity of those conditions have been excluded from the analyses. Therefore, the increase is more likely to be attributable to an increase in the proportion of cases registered. This phenomenon may be in turn attributable to higher awareness in parents and professionals (Matson & Kozlowski, 2011), better service of the agencies (Yeargin-Allsopp, Murphy, Oakley, & Sikes, 1992), more willingness to register, etc. (Lai et al., 2011). Male gender is a risk factor of SLD (Spee-van der Wekke et al., 2000; US Preventive Services Task Force, 2006; Harrison & McLeod, 2010), and more than two decades ago, a study of a national sample of 9854 Israeli Jewish children aged 2 to 3 years who were born in 1980 had found that speech and language disorders were more prevalent among male children (Bendel, Palti, Winter, & Ornoy, 1989). In Taiwan, we observed rate ratios between 1.50 and 1.83, and the range is compatible with the
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ratio observed in the Second National Sample Survey on Disability of the Mainland China—0.61% vs. 0.46% (Zheng et al., 2008). Likewise, a study report on a demographically representative population sample of 7218 children 6 years of age in the United States showed that the prevalence of speech delay was approximately 1.5 times more prevalent in boys (4.5% vs. 3.1%) and that of language impairment was also more prevalent in boys (14.2% vs. 11.9%) (Shriberg et al., 1999). A literature review conducted by the authors of that report found that the male-to-female rate ratios of moderate to severe speech delay of unknown origin ranged from 1.5 to 2.4 in five studies on children 5 to 8 years of age. With a wider age range, data from the 1995 Australian Health Survey on children aged 0–14 years also showed that boys had a higher prevalence of speech disorders (Keating et al., 2001). Furthermore, a study on 13,182 school beginners in Bavaria, Germany found boys had higher prevalence for all three types of speech impairments: 17.8% vs. 9.5% for pronunciation, 5.1% vs. 2.8% for grammar, and 4.1% vs. 2.0% for rhythm of speech (Stich, Baune, Caniato, Mikolajczyk, & Kra¨mer, 2012). While it is well documented that more boys than girls have SLD, the underlying mechanisms are unclear. In general, boys lag girls in speech and language development, and the Dunedin studies (Silva, 1987) found that the girls began to talk a month earlier than the boys on average and that they gained significantly higher scores on all the language tests. Bias in ascertainment has also been noted, as boys usually receive greater attention, are charged with higher family expectations, and have more behavior problems than girls, and therefore they are more likely to be referred for services and be reported (Shriberg et al., 1999). However, as gender equality has been improving over the years in Taiwan, such an ascertainment bias should decrease over time and lead to a decreasing trend in the boy-to-girl prevalence ratio, instead of an increasing tread as observed in our study. Further study identifying the risk factors that contributed to the increasing trend may help the prevention of SLD in the future. From 2004 to 2010, the prevalence rates of SLD were higher in rural areas in Taiwan, and the rate ratios ranged from 1.35 to 1.71. The findings are compatible with those of the Second National Sample Survey on Disability of China, in which the ratio was 1.52 (0.60% vs. 0.40%) (Zheng et al., 2008). However, a study on a demographically representative population sample of 6-year-old children in the United States observed a positive association between urbanization and the prevalence of speech delay: 4.9% in urban areas, 3.7% in suburban areas, and 2.3% in rural areas (Shriberg et al., 1999). We speculate that in less developed countries where maternal health and childhood education play important roles in the etiology of SLD, the prevalence of SLD has a negative association with urbanization, but in far developed countries where diagnosis and reporting are important factors affecting the prevalence, the association becomes positive. For example, the 1995 Australian Health Survey on children aged 0–14 years found no relationship between socioeconomic status and childhood speech disorders (Keating et al., 2001), but studies in the developing countries frequently observed a negative association (Hamdan & Al-Akhras, 2009; Zheng et al., 2008). Such international comparisons may help identifying the risk factors for SLD and cast some light on the prevention strategy. The major limitation of our study is that we used ‘‘administrative prevalence’’ data, which do not include persons who did not receive services provided by the administration. Moreover, we did not have incidence data, and this limits the identification of risk factors (Lai et al., 2011). In addition, patients with less serious disabilities that did not meet the certification criteria were not included in our analyses. In fact, with one-by-one screening and tests, a study of 410 children 5 to 6 years old sampled from two municipals of Taiwan identified 22 as having developmental speech and language disorders, yielding a prevalence rate of 6.1% (Cheng, Chen, Tsai, Chen, & Cherng, 2009), which is closer to the prevalence reported in other developed countries. Therefore, our results can be generalized to severe cases of SLD only. Furthermore, the government does not release the individual data, which makes it impossible to explore related issues in greater details. Nonetheless, in comparison with previous studies, the current study has some unique features. First of all, this study provides data at the national level. Besides the large number of cases (1637 cases in 2010 alone for example) that can offer stable statistical estimates, it can facilitate unbiased international comparisons, which is important in identifying the risk factors and constructing prevention strategies. In addition, all the cases were closely observed and then certified by physicians, making the diagnosis reliable. Furthermore, the duration of data collection lasted for 7 years, not just one as in most large-scale studies, and this allowed us to assess the time trend, which is rarely assessed in the previous studies. 5. Conclusions While a previous study found that the overall (both genders combined) prevalence of SLD in Taiwan had a constant increasing trend from 2000 to 2011, in this study, we found that the prevalence of SLD in Taiwan generally increased from 2004 to 2010 in all age groups, with the age group 3–5 years having the highest prevalence rate. Like studies in most countries in the world, the prevalence rates are higher in boys than in girls, and the rate ratio had an increasing trend over time. Further study identifying the risk factors that contributed to the differences between the two genders may help the prevention of SLD in the future. The prevalence rates are higher in rural areas than in urban areas, which is similar to many studies in developing countries but not consistent with most studies in developed countries. Likewise, the prevalence rate ratio of rural areas to urban areas had an increasing trend over time. Further international comparisons may help identifying the risk factors for SLD and cast some light on the prevention strategy. Whereas our study has provided data at the national level, which are rarely available, further analyses of the individual data are desirable.
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Acknowledgments We would like to thank Department of Statistics of Ministry of the Interior for providing the registry data and Mr. ChengHsing Yeh at the Ditmanson Medical Foundation Chia-Yi Christian Hospital for his assistance in statistical analysis.
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