Qual Life Res DOI 10.1007/s11136-014-0660-5
BRIEF COMMUNICATION
Translation, cross-cultural adaptation and validation of the Bulgarian version of the Dizziness Handicap Inventory Spaska Georgieva-Zhostova • Ognyan I. Kolev Katerina Stambolieva
•
Accepted: 20 February 2014 Ó Springer International Publishing Switzerland 2014
Abstract Purpose The aim of the present study was the translation, cross-cultural adaptation and validation of the Dizziness Handicap Inventory in Bulgarian language (DHI-BG). Methods Ninety-seven vestibular patients (19 men and 78 women, mean age 45.08 ± 13.85 years) took part in the investigation. All participants were asked to fill in the DHIBG. Internal consistency was estimated using Cronbach’s alpha and item-total correlation, reproducibility by calculating Bland–Altman’s limits of agreement and intraclass correlation coefficients (ICCs). Associations were estimated by Spearman’s correlation coefficients. Results The Cronbach’s alpha for the total score, functional, physical and emotional subscales of DHI-BG were 0.88, 0.75, 0.72 and 0.81. The floor and ceiling effects of the DHI-BG total scale were evaluated with respect to the limits of agreement which were ±9.4–14.53 points. Intraclass correlation coefficients (ICCs) for all scale and subscales were higher than the recommended value of 0.75 and determined good test–retest reliability. The range of items correlation for DHI-BG was from 0.27 (item 12) to 0.72 (item 3). No significant differences were observed in the Cronbach’s alpha coefficients between the DHI-BG and the original version, the German and Italian versions of the questionnaire. The most significant difference was observed in comparison with the German version of DHI. Construct
S. Georgieva-Zhostova (&) O. I. Kolev University Hospital of Neurology and Psychiatry ‘‘St. Naum’’, 4-th km, Tzarigradsko Shosse Boulevard, 1113 Sofia, Bulgaria e-mail: [email protected] K. Stambolieva Institute of Neurobiology, Bulgarian Academy of Science, Sofia, Bulgaria
validity presented a moderate correlation between Romberg coefficients and DHI-BG scores and strong correlation between all scores of DHI and the self-perceived disability. The results suggest that DHI-BG scores show a good discriminative validity between groups with different levels of self-assessed disability. Conclusion The Bulgarian version of the DHI is a reliable and valid tool in assessing the impact of dizziness on the quality of life in Bulgarian vestibular patients. Keywords Dizziness Handicap Inventory (DHI) Dizziness Disability
Introduction Dizziness is the second most common symptom after headache, with prevalence up to 25 % in the general population [1, 2]. Vestibular dizziness accounts for a quarter of all reports of dizziness [3]. The vestibular disorders affect the postural stability and have a significant negative impact on patients’ activities with physical and emotional consequences. There are many generic and disease-specific instruments for measuring the quality of life (QoL) in patient with dizziness, most of them in English. Various questionnaires such as Dizziness Handicap Inventory (DHI) [4], the University of California Los Angeles Dizziness Questionnaire (UCLA-DQ) [5], etc. are used for measuring the QoL of patients with dizziness. The most popular is the DHI. It has several translations and cross-cultural adaptations— Swedish [6], German [7], Italian [8], etc. but so far, there is not a Bulgarian version. The DHI is a reliable, comprehensively validated and clinically useful tool to measure self-perceived handicap
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Qual Life Res
associated with symptoms of dizziness and unsteadiness from a variety of causes. The aim of the present study was the translation, crosscultural adaptation and validation of the DHI in Bulgarian, thus providing a reliable instrument for measuring QoL of patients with dizziness and vertigo.
Subjects and methods Ninety-seven vestibular patients (19 men and 78 women, mean age 45.08 ± 13.85 years) took part in the investigation at their first examination and 52 of them (10 men and 42 women, mean age 45.65 ± 12.92 years) underwent a second examination after 1 week. All participants gave their written informed consent to take part in the study, which was approved by the Ethics Committee of Medical University—Sofia, conformity with Declaration of Helsinki. The patients were diagnosed after neuro-otological examination and had not a history of psychiatric or somatic illness. The diagnostic groups of patients were as follows: benign paroxysmal positional vertigo—20 patients at the first (11 at the second examination); vestibular neuritis—19 [12]; uncompensated vestibular hypo-function—18 [10]; labyrinthopathy—9 [5]; kinetosis—18 [7]; other vestibular dysfunctions—13 [7]. Patients with duration of dizziness up to 6 months were 46 (for retest 28), and 51 patients were with complaints for more than 6 months. The original DHI scale consists of 25 questions, organized in three subscales: physical (7 items), functional (9 items) and emotional (9 items). The response scale used in the DHI is ‘‘yes/sometimes/no’’ scored as ‘‘4/2/0,’’ respectively [4]. After obtaining permission from the authors [4], the English version of DHI was translated in Bulgarian by three independent medical experts with very good knowledge in English and retranslated in English by two independent translators that were uninformed about the original DHI version. The translated versions were discussed and edited according to the rules of the Bulgarian language. The Bulgarian version of DHI (DHI-BG) was first presented to ten patients with complaints of dizziness. All questions were well accepted. We added examples giving additional description only in item F12. The patients filled in the final questionnaire in the hospital in our presence. They understood all the items and did not find any difficulty in answering the questions (they did not ask for additional explanations). A static posturographic system (Synapsis posturography system, France) was used to measure the postural stability during upright stance with open (OE) and closed eyes (CE). The Romberg quotient describing the ratio CE/OE measures was calculated [9].
123
Statistical analysis Descriptive statistics were used for demographic, rating scales and questionnaire data. The frequency distribution of each item was evaluated for investigating the possible ceiling and floor effects. Cronbach’s alpha and item-total correlation (Spearman’s rank correlation coefficients) were used to determine the internal consistency of DHI-BG dimensions. In general, Cronbach’s alpha[0.7 (Nunnally’s criterion) indicates high levels of internal consistency [10]. The Spearman’s rank correlation coefficient values \0.25 was considered to be weak, and values C0.76 were considered to indicate a strong relationship [11]. Test–retest reliability was assessed by calculating the intraclass correlation coefficient (ICC) and by calculating Bland–Altman’s limits of agreement. The ICC values above 0.75 are indicative of good reliability [12]. The Mann–Whitney U test was used for estimating the difference between correlation coefficients of items in Bulgarian and the other language scales, where the correlation coefficients were transformed by Fisher’s r to z transformation. Convergent validity between DHI-BG scores and Romberg coefficients was determined by Spearman’s rank correlation. The discriminative validity was investigated by Kruskal–Wallis ANOVA. It evaluated the differences between DHI-BG scores and self-reported level of disability of the patients: mild—10, moderate—37 and severe—50 patients.. A p level \0.05 was considered as statistically significant. The analyses were made using the SPSS version 16.0 computer software.
Results No significant differences were observed in the Cronbach’s alpha coefficients between the DHI-BG and the original version [4], the German [7] and Italian [8] versions of the questionnaire. All values of Cronbach’s alpha coefficients for DHI-BG are in the range 0.72–0.88 (Table 1). A strong
Table 1 Reliability values (Cronbach’s alpha coefficients) for DHIBG compared with other language versions of DHI Internal consistency
Cronbach’s alpha DHI-BG
DHI
DHI-G
DHI-I
DHI-BG
0.88
0.89
0.90
0.92
Functional subscale
0.75
0.85
0.80
0.82
Physical subscale
0.72
0.78
0.71
0.75
Emotional subscale
0.81
0.72
0.82
0.84
DHI-BG—Bulgarian version; DHI—original US version; DHI-G— German version; DHI-I—Italian version
Qual Life Res Table 2 Distribution of the scores in the test (DHI-1) and retest (DHI-2) investigation of subgroup of 52 patients Reproducibility
DHI-BG
n
52
DHI-BG-1
DHI-BG-2
Mean differences and limits of agreement
ICC 2/1
Median (range)
Mean (SD)
Median (range)
Mean (SD)
Mean (SD)
Lower limit (95 % CI)
Upper limit (95 % CI)
(95 % CI)
69.00
60.05
66.00
57.50
(6–88)
(20.62)
(12–82)
(17.58)
2.55
-12
12
0.94
(5.99)
(-14.53 to -9.4)
(9.4–14.53)
(0.88–0.97)
Functional subscale
52
26.00 (4–36)
23.25 (8.20)
24.00 (4–36)
22.40 (7.22)
0.85 (2.75)
-5.5 (-6.35 to -4.65)
5.5 (4.65–6.35)
0.93 (0.87–0.96)
Physical subscale
52
21.00
19.65
19.00
18.75
0.9
-4.9
4.9
0.90
(0–28)
(6.31)
(6–28)
(5.16)
(2.44)
(-5.77 to -3.97)
(3.97–5.77)
(0.81–0.95)
Emotional subscale
52
16.00
17.15
15.00
16.35
0.8
-5.2
5.2
0.95
(2–34)
(9.26)
(2–34)
(8.01)
(2.59)
(-5.98 to -4.38)
(4.38–5.98)
(0.91–0.98)
SD standard deviation, CI confidence interval, ICCs intraclass correlations
positive correlation between the total DHI-BG score and subscales was observed (rs [ 0.75). The floor and ceiling effects of the DHI-BG total scale were evaluated with respect to the limits of agreement which were ±9.4–14.53 points. Out of 97 patients, 1 % had a score of \9 points and 1 % a score of [91 points. Only 5.1 % had a score[85 points and 2.1 % had a score of\15 points. The results demonstrated no obvious floor and ceiling effects (Table 2). The ICCs, which evaluate the test–retest reliability, were higher than the recommended value of 0.75 [10] and showed no significant difference between the scores (Table 2). The range of items correlation (CI-TCs) for DHI-BG was from 0.27 (item 12) to 0.72 (item 3) (Table 3). The CITCs for DHI-BG were significantly higher for item 2 and significantly lower for item 17 compared to the original DHI version (p \ 0.05) and similar to the Italian version of DHI. The most significant difference was observed in comparison with the German version (items: 1, 2, 6, 10, 14, 21, 22 and 24) (Table 3). Construct validity presented a moderate correlation between Romberg coefficients and DHI-BG scores: for the total scale rs = 0.38 (p \ 0.01), for functional subscale rs = 0.37 (p \ 0.01), for physical subscale rs = 0.3 (p \ 0.01) and for emotional subscale rs = 0.29 (p \ 0.01). The Kruskal–Wallis ANOVA with the three levels (mild, moderate and severe degree) showed significant effect of self-reported disability on the DHI-BG total score (H [2] = 64.002, p \ 0.001) and the three subscales (functional: H [2] = 57.626; p \ 0.001; physical: H [2] = 45.833; p \ 0.001; emotional: H [2] = 35.216; p \ 0.001). A post hoc Mann–Whitney U test showed significant difference in total DHI-BG scores and subscale scores between patients with mild and moderate and between patients with moderate and severe disability
(p \ 0.001). The results suggest that DHI-BG scores show a good discriminative validity between groups with different levels of self-assessment for disability, which reflects on the QoL of patients with vestibular dysfunction.
Discussion The results show that the questions in DHI-BG are well understood, well accepted and easy to answer by patients. Generally, the patients’ demographic and clinical characteristics of this study do not differ from those used in the other language versions of the scale [4, 7, 8]. The DHI-BG shows high internal consistency. The total reliability of DHI-BG is 0.88, and the Cronbach’s alpha values of the different language versions are similar. These results confirm the validity of DHI-BG. Probable explanations for this similarity are that the questions in DHI are clear and welldefined. CI-TC results correlate well with results of the original version of DHI [4], except slight difference in item 2 and item 17. Our results are close to the results obtained in the Italian version. However, we found some differences compared to the German version of DHI, mostly in ‘‘Emotional subscale.’’ That can be explained by differences in the lifestyle, temperament, communicability and culture between Bulgarians and Germans. For example, the sensation of embarrassment is typical for some Bulgarians, mostly aged 50 years and over. The social area and financial position are also important for the QoL of patients. The repeatability coefficients show that 92.5–100 % of the differences in test–retest scores of the DHI-BG total scale, as well as the three subscales, lay between two SDs [6]. ICC values exceed the recommended value of 0.75 [12] and are similar with the other DHI versions [4, 7, 8]. The strong positive correlation between the DHI scores and Romberg coefficients, as an objective measurement of
123
Qual Life Res Table 3 Corrected item-total correlation (CI-TC) coefficients in DHI-BG, DHI-I, DHI, DHI-G No.
Item
CI-TC
DHI-BG n = 97
DHI n = 106
DHI-G n = 127
DHI-I n = 50
P1
Does looking up increase your problem?
0.66
0.57
0.54
0.32*
0.43
E2
Because of your problem, do you feel frustrated?
0.64
0.69
0.34*
0.51*
0.64
F3
0.69
0.72
0.76
0.61
0.65
P4
Because of your problem, do you restrict your travel for business or recreation? Does walking down the aisle of a supermarket increase your problems?
0.26
0.46
0.39
0.48
0.31
F5
Because of your problem, do you have difficulty getting into or out of bed?
0.43
0.45
0.50
0.41
0.45
F6
Does your problem significantly restrict your participation in social activities, such as going out to dinner, going to the movies, dancing or going to parties?
0.86
0.53
0.69
0.72*
0.65
F7
Because of your problem, do you have difficulty reading?
0.48
0.41
0.44
0.36
0.58
P8
Does performing more ambitious activities such as sports, dancing and household chores (sweeping or putting dishes away) increase your problems?
0.57
0.62
0.54
0.67
0.60
E9
Because of your problem, are you afraid to leave your home without having someone accompany you?
0.54
0.59
0.43
0.49
0.67
E10
Because of your problem, have you been embarrassed in front of others?
0.51
0.49
0.46
0.27*
0.60
P11
Do quick movements of your head increase your problem?
0.48
0.33
0.51
0.41
0.54
F12
Because of your problem, do you avoid heights?
0.20
0.27
0.49
0.42
0.48
P13 F14
Does turning over in bed increase your problem? Because of your problem, is it difficult for you to do strenuous homework or yard work?
0.46 0.56
0.42 0.49
0.43 0.58
0.27 0.69*
0.40 0.64
E15
Because of your problem, are you afraid people may think you are intoxicated?
0.42
0.38
0.30
0.48
0.47
F16
Because of your problem, is it difficult for you to go for a walk by yourself?
0.35
0.51
0.62
0.57
0.62
P17
Does walking down a sidewalk increase your problem?
0.21
0.36
0.58*
0.46
0.41
E18
Because of your problem, is it difficult for you to concentrate?
0.42
0.46
0.49
0.51
0.57
F19
Because of your problem, is it difficult for you to walk around your house in the dark?
0.36
0.39
0.48
0.32
0.50
E20
Because of your problem are you afraid to stay home alone?
0.39
0.40
0.27
0.37
0.61
E21
Because of your problem. do you feel handicapped?
0.43
0.31
0.41
0.71*
0.58
E22
Has the problem placed stress on your relationships with members of your family or friends?
0.43
0.34
0.46
0.60*
0.29
E23
Because of your problem, are you depressed?
0.64
0.57
0.41
0.63
0.59
F24
Does your problem interfere with your job or household responsibilities?
0.43
0.43
0.56
0.66*
0.63
P25
Does bending over increase your problem?
0.58
0.39
0.57
0.32
0.54
DHI-BG—Bulgarian version, DHI—original US version, DHI-G—German version, DHI-I—Italian version; * significant differences between DHI-BG and other languages (Man–Whitney U test); significant level p \ 0.05
the vestibular dysfunction, and between the DHI scores and self-assessment of disability of the vestibular patients confirms the validity and sensitivity of the scale. It will be of benefit to measure responsiveness of change in the DHI-BG, in order to assess the effectiveness of treatment and vestibular rehabilitation on patients’ QoL.
reliable and valid tool in assessing the impact of dizziness on the QoL in Bulgarian vestibular patients.
Conclusion
References
The results of this study show high internal consistency and good test–retest reliability of the DHI-BG. DHI-BG is a
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Acknowledgments The authors wish to thank professor Jacobson who his permission and assistance in the process of validating the questionnaire.
1. Kroenke, K., Hoffman, R. M., & Einstadter, D. (2000). How common are various causes of dizziness? A critical review. Southern Medical Journal, 93, 160–167.
Qual Life Res 2. Yardley, L., Owen, N., Nazareth, I., et al. (1998). Prevalence and presentation of dizziness in a general practice community sample of working people. British Journal of General Practice, 48, 1131–1135. 3. Neuhauser, H. K., von Brevern, M., Radtke, A., et al. (2005). Epidemiology of vestibular vertigo: A neurotologic survey of the general population. Neurology, 65, 898–904. 4. Jacobson, G. P., & Newmann, C. W. (1990). The development of the Dizziness Handicap Inventory. Archives of Otolaryngology: Head and Neck Surgery, 116(4), 424–427. 5. Honrubia, V., Bell, T. S., Harris, M. R., et al. (1996). Quantitative evaluation of dizziness characteristics and impact on quality of life. American Journal of Otology, 17, 595–602. 6. Jarlsa¨ter, S., & Mattsson, E. (2003). Test of reliability of the Dizziness Handicap Inventory and the activities-specific Balance Confidence Scale for use in Sweden. Advances in Physiotherapy, 5, 137–144. 7. Kurre, A., Van Gool, C. J. A. W., Bastianen, C. H. G., et al. (2009). Translation, cross-cultural adaptation and reliability of
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the German version of the Dizziness Handicap Inventory. Otology & Neurotology, 30, 359–367. Nola, G., Mastardini, C., Salvi, V., et al. (2010). Validity of Italian adaptation of the Dizziness Handicap Inventory (DHI) and evaluation of the quality of life in patients with acute dizziness. Acta Otorhinolaryngologica Italica, 30, 190–197. Hufschmidt, A., Dichgans, J., Mauritz, K. H., & Hufschmidt, M. (1980). Some methods and parameters of body sway quantification and their neurological applications. Archiv fu¨r Psychiatrie und Nervenkrankheiten, 228, 135–150. Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297–334. Gill-Body, K. M., Beniato, M., & Krebs, D. E. (2000). Relationship among balance impairments, functional performance, and disability in people with peripheral vestibular hypofunction. Physical Therapy, 80, 748–758. Shrout, P. E., & Fleiss, J. L. (1979). Intraclass correlations: Uses in assessing rater reliability. Psychological Bulletin, 86, 420–428.
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BRIEF COMMUNICATION
Translation, cross-cultural adaptation and validation of the Bulgarian version of the Dizziness Handicap Inventory Spaska Georgieva-Zhostova • Ognyan I. Kolev Katerina Stambolieva
•
Accepted: 20 February 2014 Ó Springer International Publishing Switzerland 2014
Abstract Purpose The aim of the present study was the translation, cross-cultural adaptation and validation of the Dizziness Handicap Inventory in Bulgarian language (DHI-BG). Methods Ninety-seven vestibular patients (19 men and 78 women, mean age 45.08 ± 13.85 years) took part in the investigation. All participants were asked to fill in the DHIBG. Internal consistency was estimated using Cronbach’s alpha and item-total correlation, reproducibility by calculating Bland–Altman’s limits of agreement and intraclass correlation coefficients (ICCs). Associations were estimated by Spearman’s correlation coefficients. Results The Cronbach’s alpha for the total score, functional, physical and emotional subscales of DHI-BG were 0.88, 0.75, 0.72 and 0.81. The floor and ceiling effects of the DHI-BG total scale were evaluated with respect to the limits of agreement which were ±9.4–14.53 points. Intraclass correlation coefficients (ICCs) for all scale and subscales were higher than the recommended value of 0.75 and determined good test–retest reliability. The range of items correlation for DHI-BG was from 0.27 (item 12) to 0.72 (item 3). No significant differences were observed in the Cronbach’s alpha coefficients between the DHI-BG and the original version, the German and Italian versions of the questionnaire. The most significant difference was observed in comparison with the German version of DHI. Construct
S. Georgieva-Zhostova (&) O. I. Kolev University Hospital of Neurology and Psychiatry ‘‘St. Naum’’, 4-th km, Tzarigradsko Shosse Boulevard, 1113 Sofia, Bulgaria e-mail: [email protected] K. Stambolieva Institute of Neurobiology, Bulgarian Academy of Science, Sofia, Bulgaria
validity presented a moderate correlation between Romberg coefficients and DHI-BG scores and strong correlation between all scores of DHI and the self-perceived disability. The results suggest that DHI-BG scores show a good discriminative validity between groups with different levels of self-assessed disability. Conclusion The Bulgarian version of the DHI is a reliable and valid tool in assessing the impact of dizziness on the quality of life in Bulgarian vestibular patients. Keywords Dizziness Handicap Inventory (DHI) Dizziness Disability
Introduction Dizziness is the second most common symptom after headache, with prevalence up to 25 % in the general population [1, 2]. Vestibular dizziness accounts for a quarter of all reports of dizziness [3]. The vestibular disorders affect the postural stability and have a significant negative impact on patients’ activities with physical and emotional consequences. There are many generic and disease-specific instruments for measuring the quality of life (QoL) in patient with dizziness, most of them in English. Various questionnaires such as Dizziness Handicap Inventory (DHI) [4], the University of California Los Angeles Dizziness Questionnaire (UCLA-DQ) [5], etc. are used for measuring the QoL of patients with dizziness. The most popular is the DHI. It has several translations and cross-cultural adaptations— Swedish [6], German [7], Italian [8], etc. but so far, there is not a Bulgarian version. The DHI is a reliable, comprehensively validated and clinically useful tool to measure self-perceived handicap
123
Qual Life Res
associated with symptoms of dizziness and unsteadiness from a variety of causes. The aim of the present study was the translation, crosscultural adaptation and validation of the DHI in Bulgarian, thus providing a reliable instrument for measuring QoL of patients with dizziness and vertigo.
Subjects and methods Ninety-seven vestibular patients (19 men and 78 women, mean age 45.08 ± 13.85 years) took part in the investigation at their first examination and 52 of them (10 men and 42 women, mean age 45.65 ± 12.92 years) underwent a second examination after 1 week. All participants gave their written informed consent to take part in the study, which was approved by the Ethics Committee of Medical University—Sofia, conformity with Declaration of Helsinki. The patients were diagnosed after neuro-otological examination and had not a history of psychiatric or somatic illness. The diagnostic groups of patients were as follows: benign paroxysmal positional vertigo—20 patients at the first (11 at the second examination); vestibular neuritis—19 [12]; uncompensated vestibular hypo-function—18 [10]; labyrinthopathy—9 [5]; kinetosis—18 [7]; other vestibular dysfunctions—13 [7]. Patients with duration of dizziness up to 6 months were 46 (for retest 28), and 51 patients were with complaints for more than 6 months. The original DHI scale consists of 25 questions, organized in three subscales: physical (7 items), functional (9 items) and emotional (9 items). The response scale used in the DHI is ‘‘yes/sometimes/no’’ scored as ‘‘4/2/0,’’ respectively [4]. After obtaining permission from the authors [4], the English version of DHI was translated in Bulgarian by three independent medical experts with very good knowledge in English and retranslated in English by two independent translators that were uninformed about the original DHI version. The translated versions were discussed and edited according to the rules of the Bulgarian language. The Bulgarian version of DHI (DHI-BG) was first presented to ten patients with complaints of dizziness. All questions were well accepted. We added examples giving additional description only in item F12. The patients filled in the final questionnaire in the hospital in our presence. They understood all the items and did not find any difficulty in answering the questions (they did not ask for additional explanations). A static posturographic system (Synapsis posturography system, France) was used to measure the postural stability during upright stance with open (OE) and closed eyes (CE). The Romberg quotient describing the ratio CE/OE measures was calculated [9].
123
Statistical analysis Descriptive statistics were used for demographic, rating scales and questionnaire data. The frequency distribution of each item was evaluated for investigating the possible ceiling and floor effects. Cronbach’s alpha and item-total correlation (Spearman’s rank correlation coefficients) were used to determine the internal consistency of DHI-BG dimensions. In general, Cronbach’s alpha[0.7 (Nunnally’s criterion) indicates high levels of internal consistency [10]. The Spearman’s rank correlation coefficient values \0.25 was considered to be weak, and values C0.76 were considered to indicate a strong relationship [11]. Test–retest reliability was assessed by calculating the intraclass correlation coefficient (ICC) and by calculating Bland–Altman’s limits of agreement. The ICC values above 0.75 are indicative of good reliability [12]. The Mann–Whitney U test was used for estimating the difference between correlation coefficients of items in Bulgarian and the other language scales, where the correlation coefficients were transformed by Fisher’s r to z transformation. Convergent validity between DHI-BG scores and Romberg coefficients was determined by Spearman’s rank correlation. The discriminative validity was investigated by Kruskal–Wallis ANOVA. It evaluated the differences between DHI-BG scores and self-reported level of disability of the patients: mild—10, moderate—37 and severe—50 patients.. A p level \0.05 was considered as statistically significant. The analyses were made using the SPSS version 16.0 computer software.
Results No significant differences were observed in the Cronbach’s alpha coefficients between the DHI-BG and the original version [4], the German [7] and Italian [8] versions of the questionnaire. All values of Cronbach’s alpha coefficients for DHI-BG are in the range 0.72–0.88 (Table 1). A strong
Table 1 Reliability values (Cronbach’s alpha coefficients) for DHIBG compared with other language versions of DHI Internal consistency
Cronbach’s alpha DHI-BG
DHI
DHI-G
DHI-I
DHI-BG
0.88
0.89
0.90
0.92
Functional subscale
0.75
0.85
0.80
0.82
Physical subscale
0.72
0.78
0.71
0.75
Emotional subscale
0.81
0.72
0.82
0.84
DHI-BG—Bulgarian version; DHI—original US version; DHI-G— German version; DHI-I—Italian version
Qual Life Res Table 2 Distribution of the scores in the test (DHI-1) and retest (DHI-2) investigation of subgroup of 52 patients Reproducibility
DHI-BG
n
52
DHI-BG-1
DHI-BG-2
Mean differences and limits of agreement
ICC 2/1
Median (range)
Mean (SD)
Median (range)
Mean (SD)
Mean (SD)
Lower limit (95 % CI)
Upper limit (95 % CI)
(95 % CI)
69.00
60.05
66.00
57.50
(6–88)
(20.62)
(12–82)
(17.58)
2.55
-12
12
0.94
(5.99)
(-14.53 to -9.4)
(9.4–14.53)
(0.88–0.97)
Functional subscale
52
26.00 (4–36)
23.25 (8.20)
24.00 (4–36)
22.40 (7.22)
0.85 (2.75)
-5.5 (-6.35 to -4.65)
5.5 (4.65–6.35)
0.93 (0.87–0.96)
Physical subscale
52
21.00
19.65
19.00
18.75
0.9
-4.9
4.9
0.90
(0–28)
(6.31)
(6–28)
(5.16)
(2.44)
(-5.77 to -3.97)
(3.97–5.77)
(0.81–0.95)
Emotional subscale
52
16.00
17.15
15.00
16.35
0.8
-5.2
5.2
0.95
(2–34)
(9.26)
(2–34)
(8.01)
(2.59)
(-5.98 to -4.38)
(4.38–5.98)
(0.91–0.98)
SD standard deviation, CI confidence interval, ICCs intraclass correlations
positive correlation between the total DHI-BG score and subscales was observed (rs [ 0.75). The floor and ceiling effects of the DHI-BG total scale were evaluated with respect to the limits of agreement which were ±9.4–14.53 points. Out of 97 patients, 1 % had a score of \9 points and 1 % a score of [91 points. Only 5.1 % had a score[85 points and 2.1 % had a score of\15 points. The results demonstrated no obvious floor and ceiling effects (Table 2). The ICCs, which evaluate the test–retest reliability, were higher than the recommended value of 0.75 [10] and showed no significant difference between the scores (Table 2). The range of items correlation (CI-TCs) for DHI-BG was from 0.27 (item 12) to 0.72 (item 3) (Table 3). The CITCs for DHI-BG were significantly higher for item 2 and significantly lower for item 17 compared to the original DHI version (p \ 0.05) and similar to the Italian version of DHI. The most significant difference was observed in comparison with the German version (items: 1, 2, 6, 10, 14, 21, 22 and 24) (Table 3). Construct validity presented a moderate correlation between Romberg coefficients and DHI-BG scores: for the total scale rs = 0.38 (p \ 0.01), for functional subscale rs = 0.37 (p \ 0.01), for physical subscale rs = 0.3 (p \ 0.01) and for emotional subscale rs = 0.29 (p \ 0.01). The Kruskal–Wallis ANOVA with the three levels (mild, moderate and severe degree) showed significant effect of self-reported disability on the DHI-BG total score (H [2] = 64.002, p \ 0.001) and the three subscales (functional: H [2] = 57.626; p \ 0.001; physical: H [2] = 45.833; p \ 0.001; emotional: H [2] = 35.216; p \ 0.001). A post hoc Mann–Whitney U test showed significant difference in total DHI-BG scores and subscale scores between patients with mild and moderate and between patients with moderate and severe disability
(p \ 0.001). The results suggest that DHI-BG scores show a good discriminative validity between groups with different levels of self-assessment for disability, which reflects on the QoL of patients with vestibular dysfunction.
Discussion The results show that the questions in DHI-BG are well understood, well accepted and easy to answer by patients. Generally, the patients’ demographic and clinical characteristics of this study do not differ from those used in the other language versions of the scale [4, 7, 8]. The DHI-BG shows high internal consistency. The total reliability of DHI-BG is 0.88, and the Cronbach’s alpha values of the different language versions are similar. These results confirm the validity of DHI-BG. Probable explanations for this similarity are that the questions in DHI are clear and welldefined. CI-TC results correlate well with results of the original version of DHI [4], except slight difference in item 2 and item 17. Our results are close to the results obtained in the Italian version. However, we found some differences compared to the German version of DHI, mostly in ‘‘Emotional subscale.’’ That can be explained by differences in the lifestyle, temperament, communicability and culture between Bulgarians and Germans. For example, the sensation of embarrassment is typical for some Bulgarians, mostly aged 50 years and over. The social area and financial position are also important for the QoL of patients. The repeatability coefficients show that 92.5–100 % of the differences in test–retest scores of the DHI-BG total scale, as well as the three subscales, lay between two SDs [6]. ICC values exceed the recommended value of 0.75 [12] and are similar with the other DHI versions [4, 7, 8]. The strong positive correlation between the DHI scores and Romberg coefficients, as an objective measurement of
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Qual Life Res Table 3 Corrected item-total correlation (CI-TC) coefficients in DHI-BG, DHI-I, DHI, DHI-G No.
Item
CI-TC
DHI-BG n = 97
DHI n = 106
DHI-G n = 127
DHI-I n = 50
P1
Does looking up increase your problem?
0.66
0.57
0.54
0.32*
0.43
E2
Because of your problem, do you feel frustrated?
0.64
0.69
0.34*
0.51*
0.64
F3
0.69
0.72
0.76
0.61
0.65
P4
Because of your problem, do you restrict your travel for business or recreation? Does walking down the aisle of a supermarket increase your problems?
0.26
0.46
0.39
0.48
0.31
F5
Because of your problem, do you have difficulty getting into or out of bed?
0.43
0.45
0.50
0.41
0.45
F6
Does your problem significantly restrict your participation in social activities, such as going out to dinner, going to the movies, dancing or going to parties?
0.86
0.53
0.69
0.72*
0.65
F7
Because of your problem, do you have difficulty reading?
0.48
0.41
0.44
0.36
0.58
P8
Does performing more ambitious activities such as sports, dancing and household chores (sweeping or putting dishes away) increase your problems?
0.57
0.62
0.54
0.67
0.60
E9
Because of your problem, are you afraid to leave your home without having someone accompany you?
0.54
0.59
0.43
0.49
0.67
E10
Because of your problem, have you been embarrassed in front of others?
0.51
0.49
0.46
0.27*
0.60
P11
Do quick movements of your head increase your problem?
0.48
0.33
0.51
0.41
0.54
F12
Because of your problem, do you avoid heights?
0.20
0.27
0.49
0.42
0.48
P13 F14
Does turning over in bed increase your problem? Because of your problem, is it difficult for you to do strenuous homework or yard work?
0.46 0.56
0.42 0.49
0.43 0.58
0.27 0.69*
0.40 0.64
E15
Because of your problem, are you afraid people may think you are intoxicated?
0.42
0.38
0.30
0.48
0.47
F16
Because of your problem, is it difficult for you to go for a walk by yourself?
0.35
0.51
0.62
0.57
0.62
P17
Does walking down a sidewalk increase your problem?
0.21
0.36
0.58*
0.46
0.41
E18
Because of your problem, is it difficult for you to concentrate?
0.42
0.46
0.49
0.51
0.57
F19
Because of your problem, is it difficult for you to walk around your house in the dark?
0.36
0.39
0.48
0.32
0.50
E20
Because of your problem are you afraid to stay home alone?
0.39
0.40
0.27
0.37
0.61
E21
Because of your problem. do you feel handicapped?
0.43
0.31
0.41
0.71*
0.58
E22
Has the problem placed stress on your relationships with members of your family or friends?
0.43
0.34
0.46
0.60*
0.29
E23
Because of your problem, are you depressed?
0.64
0.57
0.41
0.63
0.59
F24
Does your problem interfere with your job or household responsibilities?
0.43
0.43
0.56
0.66*
0.63
P25
Does bending over increase your problem?
0.58
0.39
0.57
0.32
0.54
DHI-BG—Bulgarian version, DHI—original US version, DHI-G—German version, DHI-I—Italian version; * significant differences between DHI-BG and other languages (Man–Whitney U test); significant level p \ 0.05
the vestibular dysfunction, and between the DHI scores and self-assessment of disability of the vestibular patients confirms the validity and sensitivity of the scale. It will be of benefit to measure responsiveness of change in the DHI-BG, in order to assess the effectiveness of treatment and vestibular rehabilitation on patients’ QoL.
reliable and valid tool in assessing the impact of dizziness on the QoL in Bulgarian vestibular patients.
Conclusion
References
The results of this study show high internal consistency and good test–retest reliability of the DHI-BG. DHI-BG is a
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Acknowledgments The authors wish to thank professor Jacobson who his permission and assistance in the process of validating the questionnaire.
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