f. Child Psychol. Psychiat. Vol. 31, No. 7, pp. 1027-1050, 1990 Printed in Great Britain.
0021-9630/90 $3 00 + 0 00 Pergamon'Press pic © 1990 Association for Child Psychology and Psychiatry
A Prospective Study of the Relationship between Specific Language Impairment, Phonological Disorders and Reading Retardation D. V. M. Bishop* and C. Adams^ Abstract—Language and literacy skills were assessed in 83 8 54 -year olds whose language development had been impaired at 4 years of age. Provided that language problems had resolved by age 5 V2 years, literacy development was normal, but many of the children who still had verbal deficits at 5 V2 years of age did have reading difficulties and persisting oral language impairments later on. In these children, reading comprehension tended to be poor relative to reading accuracy. Syntactic competence in the preschool period accounted for a substantial proportion of the variance in literacy attainments, after allowing for the effects of non-verbal ability. There were only weak links between expressive phonological disorders and later ability to read either meaningful text or non-words.
Keywords: Language disorder, reading disability, phonology, prediction
Introduction Part I. Reading and Spelling Proficiency in Children with a History of Language Delay There is good evidence from several sources for a relationship between reading difficulties and impaired language development. First, longitudinal studies of children who are identified as having delayed language milestones find relatively low attainments in reading and spelling when these children are followed up at 7 or 8 years of age (Fundudis, Kolvin & Garside, 1979; Richman, Stevenson & Graham, 1982; Silva,
Accepted manuscript received 20 March 1990
*Department of Psychology, University of Manchester, Manchester M13 9PL, U.K. ^Present address: Centre of Audiology, Education of the Deaf and Speech Pathology, University of Manchester, Manchester, U.K. Requests for reprints to: Dr D. V. M. Bishop, Department of Psychology, University of Manchester, Manchester M13 9PL, U.K.
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D. V. M. Bishop and C. Adams
Williams & McGee, 1987). Second, retrospective studies report that an unusually high proportion of children with specific reading disability were late in starting to talk (Kinsbourne & Warrington, 1963; Naidoo, 1972; Rutter, Tizard & Whitmore, 1970). Furthermore, experimental studies of children with specific reading disability have found evidence of continuing verbal deficits, especially in tasks involving phonological processing, even in children who have no immediately obvious signs of language disorder (see reviews by Jorm & Share, 1983; Snowling, 1987). On the basis of these studies one might predict that a child who has a specific language impairment in the preschool period will be at high risk for specific reading disability later on, even if the obvious problems with spoken language have resolved. In 1987, Bishop and Edmundson reported results from a longitudinal study of children who were identified as having language impairment at the age of 4 years, who were followed up to 5 ^ years of age. We report here results from a further followup of this sample carried out between 1986 and 1988, when these children were 8 ^ -years old. The follow-up assessment included tests of reading and spelling, making it possible to investigate further the nature of the link between early language delay and later literacy problems.
Method Subfects
Language-delayed sample
The study sample was described in detail by Bishop and Edmundson (1987a). Between 1982 and 1984, paediatricians and speech therapists were asked to refer children aged between the ages of 3:9 and 4:2 who had any impairment of language development that could not be attributed to low intelligence, hearing loss, physical defect or bilingual background, and which was not associated with a recognized syndrome such as infantile autism. Eighty-eight children were recruited to the study, of whom 19 (the 'general delay' subgroup) were identified as having delayed non-verbal development on the basis of a shortened version of the Leiter International Performance Scale (Leiter, 1948). The remaining children were designated as having 'specific language impairment' (SLI). All but one of these children were followed up at the age of 4i/4 years and again at 5 ^ years, by which time 32 of them no longer had any evidence of language impairment. In line with the terminology adopted by Bishop and Edmundson, these children will be referred to here as the group with good outcome at 5 years. The remaining children are classified as having poor outcome at 5 years. In classifying children into these subgroups, we do not wish to imply that there are sharp divisions between those with good and poor outcomes, or those with specific and non-specific developmental delays. Indeed, our own analyses support the idea that differences between these subgroups are quantitative rather than qualitative (Bishop & Edmundson, 1987b). However, the distinction can be of use when considering clinical implications of the study, where one wishes to ask such questions as whether language-delayed children who appear to have recovered by 5 J^ years will go on to have literacy problems. Eighty-three (94.3%) of the children studied by Bishop and Edmundson were seen again at the age of 8/2 years (mean age 100 months, S.D. 1.2 months). One child had been discovered to have a high frequency hearing loss at the age of 6 years, and her data are not included here. Parents of the four remaining children were unwilling for their child to participate further in the study. Control group
A sample of 30 control 8-year olds, matched with the experimental group in terms of sex ratio (22 boys and 8 girls), was given a shortened version of the test battery to provide normative standards
Language impairment and reading retardation
1029
for some of the unstandardized measures. Twenty of these children came from a primary school in inner-city Manchester and 10 from a rural town in Lancashire. In addition, we also made use of WISC-R and reading data gathered by Bishop and Butterworth (1979, 1980) on an unselected sample of 168 8>/2-year olds. These data were used to compute the regressions of reading ability on WISC-R subtests, and to predict reading comprehension on the basis of reading accuracy (see below).
Materials Non-verbal ability
At the first assessment, when children were aged 4 years, a shortened version of the Leiter International Performance Scale was administered, scores being transformed to scaled scores on the basis of normative data from a control group of 4-year olds. At 8 J4 years of age, two WISC-R performance subtests, picture completion and block design (Wechsler, 1974), were administered. Receptive vocabulary
The British Picture Vocabulary Scale (BPVS; Dunn, Dunn, Whetton & Pintilie, 1982), a British version of the Peabody Picture Vocabulary Test, was used at each assessment to measure receptive vocabulary. The child selects from an array the picture that matches a word spoken by the tester. Scores were converted to standard scores with a mean of 100 and S.D. of 15 (based on standardization data). Understanding of grammatical contracts
The Test for Reception of Grammar (TROG) (Bishop, 1989) was administered at each assessment. This is a multiple-choice test in which the child is required to select from an array the picture that matches a phrase or sentence spoken by the tester. Vocabulary is kept simple, but grammatical complexity increases as the test proceeds. The test is scored in terms of number of blocks correct out of 20, with each block of four items testing comprehension of a particular type of grammatical contrast. Logarithmic error scores were converted to standard scores with a mean of 100 and S.D. of 15 (based on standardization data). General comprehension
In the first three assessment sessions, the BAS verbal comprehension subtest (Elliott, Murray & Pearson, 1978) was administered as a general measure of ability to carry out instructions. As norms for this subtest do not extend beyond 4 years, 11 months, scores were transformed to scaled scores for the first two test sessions only. At the follow-up assessment at 8V2 years, the WISC-R verbal comprehension subtest was included. Unlike the other two comprehension tests (BPVS and TROG), which simply involve matching the literal meaning of a word or sentence to an item from an array, this subtest requires the child to use general and social knowledge to work out appropriate answers to questions. Scores were transformed to standard scores with a mean of 100 and S.D. of 15 (based on standardization data). Expressive phonology
In the first three assessments, a set of photographs (Newcastle speech assessment) was given to the child to name in order to elicit a wide range of consonants and consonant clusters. Responses were transcribed by the tester, who was trained in phonetic transcription. For the 8 5^-year old follow-up, responses to the Word-Finding Vocabulary Scale (see below) were used to identify phonological errors in children's speech. Phonological errors when naming were transcribed, and the child's total responses to the test were analysed to compute the percentage of consonants correct (Shriberg & Kwiatkowski, 1982).
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D. V. M. Bishop and C. Adams
Expressive vocabulary
In the first three assessments, the BAS naming vocabulary subtest (Elliott et al., 1978) was administered, scores being converted to standard scores. For the 8 Vz -year old assessment we used Renfrew's Word-Finding Vocabulary Scale (Renfrew, 1980), a confrontation picture-naming test suitable for children of this age. Our own control data were used to convert scores into standard scores based on a mean of 100 and S.D. of 15. Mean length of utterance (ML U)
For the first three assessments, MLU (in morphemes) was computed from all utterances given as responses to the Action Picture Test (Renfrew, 1966) and the Bus Story Test (Renfrew, 1969). Control data from children of the same age were used to convert scores to standard scores. Lack of an adequately standardized procedure suitable for older children led us to formulate our own test materials for the 8J4-year old assessment. A commercially available picture-book {Not Now, Bernard, David McKee, 1980) was modified to give a story which could be told to the child with pictures before asking him or her to go through the pictures again retelling the story. The child's story was tape-recorded and transcribed by one of the authors, and used to compute MLU in morphemes. Control data gathered in this study were used to transform scores into standard scores with a mean of 100 and S.D. of 15. Expression of semantic relations
T,he Bus Story information score was used as an index of the ability to express semantic relationships at 4, 4J4 and bYz years. Control data were used to transform scores to standard scores. The Not Now Bernard story, used at 8 /4 years, was also analysed for semantic content. Each phrase in the story was coded according to whether it described a central idea of the story or an incidental detail, and the child's account was credited 2 points for each central idea and 1 point for each incidental detail mentioned. Alterations in wording were credited provided the basic meaning was preserved. Our own control data were used to transform scores into standard scores with a mean of 100 and S.D. of 15. Reading ability
The Neale Analysis of Reading Ability, form C (Neale, 1966), was administered at the follow-up assessment at 8 ^ years. The child reads short stories of increasing difficulty until 12 or more errors are made on a passage. If a child does not produce a response to a word within 4 seconds, the tester provides it and an error is scored. A set of comprehension questions is provided after each passage to assess the child's understanding of the story. Separate reading ages can be computed for accuracy and comprehension. Data from an unselected population of 168 British 8J4-year olds (mean age 101 months, S.D. 6.9 months) (Bishop & Butterworth, 1979, 1980) were used as a basis for converting scores to standard scores with a mean of 100 and S.D. of 15, after applying a logarithmic transform to raw reading scores to reduce skew. Mean scores from the Bishop and Butterworth sample were close to expected population values: the mean difference between reading accuracy and chronological age (in months) was - 1.25. Reading comprehension data from this population have not previously been published: the mean difference between reading comprehension age and chronological age in this sample was -0.53 months. Spelling
The Graded Word Spelling Test (Vernon, 1977) was administered at the follow-up assessment. The child is required to spell words of increasing difficulty, each of which is dictated both in the context of a sentence and in isolation. Testing is discontinued when 10 errors have been made. Published test norms (for English children) were used to transform scores to standard scores with a mean of 100 and S.D. of 15. Test of non-word spelling and reading
Sixteen non-words were prepared, eight for spelling (mim, zab, pog, tep, plom, frool, samkin, hingo) and eight for reading (bab, wob, zok, pim, stig, drune, binkol, shavim). Four items in each set were
Language impairment and reading retardation
1031
consonant-vowel-consonant monosyllables, two were monosyllables containing a consonant cluster, and two were bisyllabic. Easy early items involved one-to-one correspondences between graphemes and phonemes, but later items required knowledge of more complicated relationships between letters and sounds (e.g. long vowels, or consonants spelt by a digraph). The first two items in each set were used as practice items, which were not scored. For the spelling task, the child was presented with a card showing a line-drawing of a space monster, whose name was written on the back of the card. The tester spoke the name of the space monster and asked the child to repeat it and then to write it. For the practice items, the child was helped to work out the correct answer if errors were made. The tester recorded whether or not the child had repeated the non-word correctly. Feedback was given for all the spelling items, with the child checking the back of the card after attempting to write the name. For the reading task, the child was given cards showing a space monster and a non-word written in lower case, and asked to read adoud the name of the space monster. Feedback was given for the two practice items. Scoring of non-word reading and spelling was in terms of an error measure, phonemic distance from target, with a point being added for each phoneme represented incorrectly, omitted or added (see Bishop, 1985, for further details). The total phonemic distance was added across all non-words, giving a maximum error score of 25 for reading and 25 for spelling.
Procedure The procedures for the first three assessments are described fully by Bishop and Edmundson (1987a). Briefiy, each child was individually assessed in a single test session and given the whole battery of tests, except where lack of cooperation or inattention developed to such a point that testing had to be discontinued: in effect, this meant that some children were not given the BPVS and/or TROG at the age of 4 or 4 ^ years. For the follow-up assessment, each child in the experimental group was seen by one of the authors in a quiet room at home, school or clinic for a single session lasting from 60 to 90 minutes, in which all of the aforementioned assessments were administered. Control 8 5^2 -year olds were seen individually at their school and were given the following tests: Not Now Bernard story, WISC-R picture completion, Neale Analysis of Reading Ability, Vernon spelling test, non-word reading and spelling and Word-Finding Vocabulary Scale.
Results Mean scores on language and non-verbal tests are shown in Table 1 for control children and for language-impaired 8-year olds divided according to status at 5 ^/4 years. Scores on standardized tests for each subgroup in Table 1 were compared to mean values from normative data using one-way analyses of variance. For non-standardized tests, scores of experimental groups were compared with the control group mean using one way analysis of variance. All F-ratios were significant at the 0.01 level. The general delay group differed significantly from control values on all tests, verbal and nonverbal. The children with poor outcome at 5 years scored significantly below control values on all verbal assessments except for Vernon spelling, where the difference fell just short of statistical significance. The mean score of this group on the non-verbal block design test was significantly below the norm, but the picture completion score was not. Children with good outcome at 5 years did not differ from normal controls except on two comprehension tests, TROG and WISC-R verbal comprehension, where mean scores were significantly below those of the standardization samples. Reading ability relative to intellectual level
It can be seen from Table 1 that children with poor outcome at 5 years and those
1032
D. V. M. Bishop and C. Adams
Table 1. Mean (S.D.) scaled scores on language tests at 8 ^ years Control 30)
Age (months)
100.5
(2.94)
100.0*^ 99.9^ 97 9'* 100.5 97.9 94.1
(14.9) (14.9) (16.6) (15.1) (18.7) (16.9)
Good outcome at 5 years (^ = 29) 99.9 96.5 92.0'' 91.7 " 105.1 98.5 100.4 105.2 102.0 96.4 105.0 101.7
BPVS TROG Verbad comprehension Word-finding
MLU Expressive semantics Reading accuracy Reading comprehension Spelling Block design Picture completion
98.7 (13.5)
"Significantly below control/normative value, '^Used as basis for computing scaled scores.
(0.86) (11.8) (13.0) (16.3) (11.2) (17.4) (17.2) (12.3) (12.6) (21.3) (12.4) (12.4)
Poor outcome at 5 years (A^=37)
General delay (A^= 16)
100.1 (1.35) 83.6"(13.6) 81.1" (9.4) 78.1" (12.2) 83.5" (16.3) 85.0" (18.4) 77.8" (17.9) 89.0" (14.6) 84.0" (14.9) 83.0 (12.8) 91.5" (17.2) 94.1 (11.6)
99.8 (1.24) 76.1"(15.2) 74.8" (7.8) 72.5" (12.2) 73.0" (19.0) 78.6" (19.0) 64.3" (12.7) 80.2" (20.2) 72.6" (18.6) 77.5" (12.4) 87.5"(25.7) 85.9" (12.6)
p u
120-
re u u re
10080-
re
6040 40
60
80
100
120
140
160
block design •«• picture completion
Fig. 1. Scatterplot showing relationship between non-verbal ability and reading accuracy at 8}-^ years for the language-delayed group. The regression hnes for control and language-delayed groups are also shown: the control line is the higher one. Both non-verbal ability and reading ability are shown as scaled scores with a mean of 100 and S.D. of 15. (D) Good outcome at 5 years; ( B ) poor outcome at 5 years; (A) general delay.
1033
Language impairment and reading retardation
reading accuracy from non-verbal ability for these two groups, with the languagedelayed group coded according to 5}/2-year old status. Neither the slopes nor the intercepts of these lines differed significantly. For reading accuracy, the adjusted scaled scores were 99.45 for the controls and 97.05 for the language-delayed sample. A different picture was obtained when reading comprehension scores were considered. Regression lines for control and language-delayed children are shown in Fig. 2, together with data points for individual children in the language-delayed sample. Slopes of the two lines did not differ significantly, but the intercepts were significantly different [F(l, 230) = 6.6; /)< 0.05]. The adjusted mean reading comprehension score for the control group was 99.39, and for the language-delayed group, 92.54. I4U -
o "w a> a>
D
120-
c CO
°
^
^
•
100-
D •
uo
•
••
-X"^ •
80-
4040
A
•
1 BA •• • • AAD •
•
60-
jJ2P;jcf^°D
• • •
A
AA
A
•
A 1
60
1
80
1
100
1
1
120
140
160
block design + picture completion
Fig. 2. Scatterplot showing relationship between non-verbal ability and reading comprehension at 8'/2 years for language-delayed group. The regression lines for control and language-delayed groups are also shown: the control line is the higher one. Both non-verbal ability and reading ability are shown as scaled scores with a mean of 100 and S.D. of 15. (CH) Good outcome at 5 years; ( H ) poor outcome at 5 years; (A) general delay.
These results suggest that children in the language-delayed group obtain reading comprehension scores that are disproportionately poor relative to their reading accuracy. A further analysis of covariance confirmed this impression: reading comprehension scores of language-delayed and control groups were compared after adjusting for reading accuracy. The effect of group was highly significant \F (1, 230) = 26.31; Thus when non-verbal ability is taken into account, the language-delayed group does not differ from the control group on reading accuracy, but is impaired on reading comprehension. The next question to ask is whether this deficit in comprehension is specific to written language, or whether it is one aspect of more general verbal impairment. It was noted above that the language-delayed children tended to do poorly on WISC-R verbal comprehension. To see how far poor reading scores could be explained in terms of this, a further analysis of covariance was carried out, this time adjusting reading scores relative to verbal as well as non-verbal ability, by using the summed scaled scores of all three WISC-R subtests (block design, picture completion
1034
D. V. M. Bishop and C. Adams
aind verbal comprehension) as covariate. There was no significant effect of group for either reading accuracy [F(l, 230) < l] or reading comprehension [F(l, 230) = 1.57]. We may conclude that the poor reading comprehension scores obtained by the language-delayed group can be explained in terms of their generally poor level of language understanding. Ability to read and spell non-words
Although the reading accuracy scores were very similar for those with good outcome at 5 years and the control group, it could be that the two groups were using different strategies to read. In particular, we were interested in the possibility that the children with a history of SLI might have difficulty learning phonics and so might rely more heavily on learning whole orthographic patterns, in which case they should be especially poor at non-word reading. Non-word error data are shown in Table 2. A logarithmic transformation was applied to non-word error data to stabilize variances, and a twoway analysis of variance used to compare the control group with the three subgroups of language-delayed children, treating non-word reading/spelling as a repeated measure. There was a highly significant main effect of group {F = 10.96; d.f. = 3, 108; p < 0.01) and of read/speU (F = 22.31; d.f = 1, 108; p < 0.01), but the interaction was not significant. The overall score of children with poor outcome at 5 years and those with general delay was significantly below that of control children and the group with good outcome at 5 years, who did not differ significantly from one another. Table 2. Mean (S.D.) phoneme errors (out of 25) in reading and spelling non-words
(A^=30)
Good outcome at 5 years (^ = 29)
Poor outcome at 5 years (A^=37)
General delay (N= 16)
7.7 (7.79)
5.3 (5.87)
12.3 (7.0)
16.1 (9.45)
5.7 (6.38)
3.4 (3.84)
8.1 (6.14)
16.3 (10.27)
Control
Non-word reading Non-word spelling
The scatterplot relating Neale reading accuracy to non-word reading errors is shown in Fig. 3. If the experimental group had disproportionate difficulty with non-word processing, their scores should cluster below the control regression line. It is clear from inspection that this is not the case. An analysis of covariance confirmed that neither the slopes nor the intercepts of the regression lines for predicting non-word errors from reading accuracy differed between control and language-delayed groups (all F-ratios< 1). How many children are reading retarded?
The above analyses make it clear that the numbers of children classified as reading retarded will depend crucially on the definition adopted. Although not all authors accept this procedure (e.g. Siegel, 1988), it is common for a distinction to be drawn between those children whose low reading attainments
1035
Language impairment and reading retardation
>u a
(0
'•3
-2 o o
40
60
80
100
120
140
Neale reading accuracy (scaled)
Fig. 3. Scatterplot showing relationship between Neale reading accuracy and non-word reading accuracy. The plotted line is the regression of non-word reading on reading accuracy for controls. ( x ) Control; (D) good outcome at 5 years; ( I ) poor outcome at 5 years; (A) general delay.
are compatible with their limited intelligence, and those poor readers of normal intelligence. Yule and Rutter (1976) have recommended defining specific reading retardation (SRR) in terms of the regression equation relating reading ability to I.Q. A child whose reading score is significantly below the level predicted from I.Q. is regarded as specific2dly reading retarded, whereas one whose reading is poor but consistent with I.Q. is termed a 'backward reader'. Using the control regression lines relating non-verbal ability to reading accuracy and comprehension (see Figs 1 and 2), children in the language-delayed sample were categorized as follows. SRR: A—specific reading retarded on accuracy: this group consisted of children whose obtained reading accuracy was more than 1.96 S.D.s below the value predicted from their summed block design and picture completion scores. SRR:C—specific reading retarded on comprehension: these were children whose obtained reading comprehension was more than 1.96 S.D.s below the value predicted from their summed block design and picture completion scores. BR—backward readers: these were children whose reading scaled score was below 71 on either scale, but who did not fall into either SRR group. (In Bishop and Butterworth's normal sample, 3% of children fell into this category.) All those who did not fit the criteria for one of these categories were classed together as normal readers. Note that the two categories of SRR are not mutually exclusive. Five children met the criteria for both SRR: A and SRR:C. Two of these had poor outcome at 5 years and three were from the general delay group. Two children (both with poor outcome at 5 years) were included in the category SRR:A but not SRR:C, and five children (one good outcome at 5 years, one poor outcome at 5 years, and three general delay) met criteria for SRR:C but not SRR:A. Overall, seven out of 82 children (8%) met
1036
D. V. M. Bishop and C. Adams
criteria for SRR:A, and 10 (12%) met criteria for SRR:C. In the general population we would predict that 5% of children should fall in each category. The frequency of SRR:A is not significantly different from expectation (chi-square with Yates' correction = 1.48, d.f = 1), but the frequency of SRR:C is significantly above expectation (chi-square = 7.49, d.f. = 1, p
0021-9630/90 $3 00 + 0 00 Pergamon'Press pic © 1990 Association for Child Psychology and Psychiatry
A Prospective Study of the Relationship between Specific Language Impairment, Phonological Disorders and Reading Retardation D. V. M. Bishop* and C. Adams^ Abstract—Language and literacy skills were assessed in 83 8 54 -year olds whose language development had been impaired at 4 years of age. Provided that language problems had resolved by age 5 V2 years, literacy development was normal, but many of the children who still had verbal deficits at 5 V2 years of age did have reading difficulties and persisting oral language impairments later on. In these children, reading comprehension tended to be poor relative to reading accuracy. Syntactic competence in the preschool period accounted for a substantial proportion of the variance in literacy attainments, after allowing for the effects of non-verbal ability. There were only weak links between expressive phonological disorders and later ability to read either meaningful text or non-words.
Keywords: Language disorder, reading disability, phonology, prediction
Introduction Part I. Reading and Spelling Proficiency in Children with a History of Language Delay There is good evidence from several sources for a relationship between reading difficulties and impaired language development. First, longitudinal studies of children who are identified as having delayed language milestones find relatively low attainments in reading and spelling when these children are followed up at 7 or 8 years of age (Fundudis, Kolvin & Garside, 1979; Richman, Stevenson & Graham, 1982; Silva,
Accepted manuscript received 20 March 1990
*Department of Psychology, University of Manchester, Manchester M13 9PL, U.K. ^Present address: Centre of Audiology, Education of the Deaf and Speech Pathology, University of Manchester, Manchester, U.K. Requests for reprints to: Dr D. V. M. Bishop, Department of Psychology, University of Manchester, Manchester M13 9PL, U.K.
1027
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D. V. M. Bishop and C. Adams
Williams & McGee, 1987). Second, retrospective studies report that an unusually high proportion of children with specific reading disability were late in starting to talk (Kinsbourne & Warrington, 1963; Naidoo, 1972; Rutter, Tizard & Whitmore, 1970). Furthermore, experimental studies of children with specific reading disability have found evidence of continuing verbal deficits, especially in tasks involving phonological processing, even in children who have no immediately obvious signs of language disorder (see reviews by Jorm & Share, 1983; Snowling, 1987). On the basis of these studies one might predict that a child who has a specific language impairment in the preschool period will be at high risk for specific reading disability later on, even if the obvious problems with spoken language have resolved. In 1987, Bishop and Edmundson reported results from a longitudinal study of children who were identified as having language impairment at the age of 4 years, who were followed up to 5 ^ years of age. We report here results from a further followup of this sample carried out between 1986 and 1988, when these children were 8 ^ -years old. The follow-up assessment included tests of reading and spelling, making it possible to investigate further the nature of the link between early language delay and later literacy problems.
Method Subfects
Language-delayed sample
The study sample was described in detail by Bishop and Edmundson (1987a). Between 1982 and 1984, paediatricians and speech therapists were asked to refer children aged between the ages of 3:9 and 4:2 who had any impairment of language development that could not be attributed to low intelligence, hearing loss, physical defect or bilingual background, and which was not associated with a recognized syndrome such as infantile autism. Eighty-eight children were recruited to the study, of whom 19 (the 'general delay' subgroup) were identified as having delayed non-verbal development on the basis of a shortened version of the Leiter International Performance Scale (Leiter, 1948). The remaining children were designated as having 'specific language impairment' (SLI). All but one of these children were followed up at the age of 4i/4 years and again at 5 ^ years, by which time 32 of them no longer had any evidence of language impairment. In line with the terminology adopted by Bishop and Edmundson, these children will be referred to here as the group with good outcome at 5 years. The remaining children are classified as having poor outcome at 5 years. In classifying children into these subgroups, we do not wish to imply that there are sharp divisions between those with good and poor outcomes, or those with specific and non-specific developmental delays. Indeed, our own analyses support the idea that differences between these subgroups are quantitative rather than qualitative (Bishop & Edmundson, 1987b). However, the distinction can be of use when considering clinical implications of the study, where one wishes to ask such questions as whether language-delayed children who appear to have recovered by 5 J^ years will go on to have literacy problems. Eighty-three (94.3%) of the children studied by Bishop and Edmundson were seen again at the age of 8/2 years (mean age 100 months, S.D. 1.2 months). One child had been discovered to have a high frequency hearing loss at the age of 6 years, and her data are not included here. Parents of the four remaining children were unwilling for their child to participate further in the study. Control group
A sample of 30 control 8-year olds, matched with the experimental group in terms of sex ratio (22 boys and 8 girls), was given a shortened version of the test battery to provide normative standards
Language impairment and reading retardation
1029
for some of the unstandardized measures. Twenty of these children came from a primary school in inner-city Manchester and 10 from a rural town in Lancashire. In addition, we also made use of WISC-R and reading data gathered by Bishop and Butterworth (1979, 1980) on an unselected sample of 168 8>/2-year olds. These data were used to compute the regressions of reading ability on WISC-R subtests, and to predict reading comprehension on the basis of reading accuracy (see below).
Materials Non-verbal ability
At the first assessment, when children were aged 4 years, a shortened version of the Leiter International Performance Scale was administered, scores being transformed to scaled scores on the basis of normative data from a control group of 4-year olds. At 8 J4 years of age, two WISC-R performance subtests, picture completion and block design (Wechsler, 1974), were administered. Receptive vocabulary
The British Picture Vocabulary Scale (BPVS; Dunn, Dunn, Whetton & Pintilie, 1982), a British version of the Peabody Picture Vocabulary Test, was used at each assessment to measure receptive vocabulary. The child selects from an array the picture that matches a word spoken by the tester. Scores were converted to standard scores with a mean of 100 and S.D. of 15 (based on standardization data). Understanding of grammatical contracts
The Test for Reception of Grammar (TROG) (Bishop, 1989) was administered at each assessment. This is a multiple-choice test in which the child is required to select from an array the picture that matches a phrase or sentence spoken by the tester. Vocabulary is kept simple, but grammatical complexity increases as the test proceeds. The test is scored in terms of number of blocks correct out of 20, with each block of four items testing comprehension of a particular type of grammatical contrast. Logarithmic error scores were converted to standard scores with a mean of 100 and S.D. of 15 (based on standardization data). General comprehension
In the first three assessment sessions, the BAS verbal comprehension subtest (Elliott, Murray & Pearson, 1978) was administered as a general measure of ability to carry out instructions. As norms for this subtest do not extend beyond 4 years, 11 months, scores were transformed to scaled scores for the first two test sessions only. At the follow-up assessment at 8V2 years, the WISC-R verbal comprehension subtest was included. Unlike the other two comprehension tests (BPVS and TROG), which simply involve matching the literal meaning of a word or sentence to an item from an array, this subtest requires the child to use general and social knowledge to work out appropriate answers to questions. Scores were transformed to standard scores with a mean of 100 and S.D. of 15 (based on standardization data). Expressive phonology
In the first three assessments, a set of photographs (Newcastle speech assessment) was given to the child to name in order to elicit a wide range of consonants and consonant clusters. Responses were transcribed by the tester, who was trained in phonetic transcription. For the 8 5^-year old follow-up, responses to the Word-Finding Vocabulary Scale (see below) were used to identify phonological errors in children's speech. Phonological errors when naming were transcribed, and the child's total responses to the test were analysed to compute the percentage of consonants correct (Shriberg & Kwiatkowski, 1982).
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D. V. M. Bishop and C. Adams
Expressive vocabulary
In the first three assessments, the BAS naming vocabulary subtest (Elliott et al., 1978) was administered, scores being converted to standard scores. For the 8 Vz -year old assessment we used Renfrew's Word-Finding Vocabulary Scale (Renfrew, 1980), a confrontation picture-naming test suitable for children of this age. Our own control data were used to convert scores into standard scores based on a mean of 100 and S.D. of 15. Mean length of utterance (ML U)
For the first three assessments, MLU (in morphemes) was computed from all utterances given as responses to the Action Picture Test (Renfrew, 1966) and the Bus Story Test (Renfrew, 1969). Control data from children of the same age were used to convert scores to standard scores. Lack of an adequately standardized procedure suitable for older children led us to formulate our own test materials for the 8J4-year old assessment. A commercially available picture-book {Not Now, Bernard, David McKee, 1980) was modified to give a story which could be told to the child with pictures before asking him or her to go through the pictures again retelling the story. The child's story was tape-recorded and transcribed by one of the authors, and used to compute MLU in morphemes. Control data gathered in this study were used to transform scores into standard scores with a mean of 100 and S.D. of 15. Expression of semantic relations
T,he Bus Story information score was used as an index of the ability to express semantic relationships at 4, 4J4 and bYz years. Control data were used to transform scores to standard scores. The Not Now Bernard story, used at 8 /4 years, was also analysed for semantic content. Each phrase in the story was coded according to whether it described a central idea of the story or an incidental detail, and the child's account was credited 2 points for each central idea and 1 point for each incidental detail mentioned. Alterations in wording were credited provided the basic meaning was preserved. Our own control data were used to transform scores into standard scores with a mean of 100 and S.D. of 15. Reading ability
The Neale Analysis of Reading Ability, form C (Neale, 1966), was administered at the follow-up assessment at 8 ^ years. The child reads short stories of increasing difficulty until 12 or more errors are made on a passage. If a child does not produce a response to a word within 4 seconds, the tester provides it and an error is scored. A set of comprehension questions is provided after each passage to assess the child's understanding of the story. Separate reading ages can be computed for accuracy and comprehension. Data from an unselected population of 168 British 8J4-year olds (mean age 101 months, S.D. 6.9 months) (Bishop & Butterworth, 1979, 1980) were used as a basis for converting scores to standard scores with a mean of 100 and S.D. of 15, after applying a logarithmic transform to raw reading scores to reduce skew. Mean scores from the Bishop and Butterworth sample were close to expected population values: the mean difference between reading accuracy and chronological age (in months) was - 1.25. Reading comprehension data from this population have not previously been published: the mean difference between reading comprehension age and chronological age in this sample was -0.53 months. Spelling
The Graded Word Spelling Test (Vernon, 1977) was administered at the follow-up assessment. The child is required to spell words of increasing difficulty, each of which is dictated both in the context of a sentence and in isolation. Testing is discontinued when 10 errors have been made. Published test norms (for English children) were used to transform scores to standard scores with a mean of 100 and S.D. of 15. Test of non-word spelling and reading
Sixteen non-words were prepared, eight for spelling (mim, zab, pog, tep, plom, frool, samkin, hingo) and eight for reading (bab, wob, zok, pim, stig, drune, binkol, shavim). Four items in each set were
Language impairment and reading retardation
1031
consonant-vowel-consonant monosyllables, two were monosyllables containing a consonant cluster, and two were bisyllabic. Easy early items involved one-to-one correspondences between graphemes and phonemes, but later items required knowledge of more complicated relationships between letters and sounds (e.g. long vowels, or consonants spelt by a digraph). The first two items in each set were used as practice items, which were not scored. For the spelling task, the child was presented with a card showing a line-drawing of a space monster, whose name was written on the back of the card. The tester spoke the name of the space monster and asked the child to repeat it and then to write it. For the practice items, the child was helped to work out the correct answer if errors were made. The tester recorded whether or not the child had repeated the non-word correctly. Feedback was given for all the spelling items, with the child checking the back of the card after attempting to write the name. For the reading task, the child was given cards showing a space monster and a non-word written in lower case, and asked to read adoud the name of the space monster. Feedback was given for the two practice items. Scoring of non-word reading and spelling was in terms of an error measure, phonemic distance from target, with a point being added for each phoneme represented incorrectly, omitted or added (see Bishop, 1985, for further details). The total phonemic distance was added across all non-words, giving a maximum error score of 25 for reading and 25 for spelling.
Procedure The procedures for the first three assessments are described fully by Bishop and Edmundson (1987a). Briefiy, each child was individually assessed in a single test session and given the whole battery of tests, except where lack of cooperation or inattention developed to such a point that testing had to be discontinued: in effect, this meant that some children were not given the BPVS and/or TROG at the age of 4 or 4 ^ years. For the follow-up assessment, each child in the experimental group was seen by one of the authors in a quiet room at home, school or clinic for a single session lasting from 60 to 90 minutes, in which all of the aforementioned assessments were administered. Control 8 5^2 -year olds were seen individually at their school and were given the following tests: Not Now Bernard story, WISC-R picture completion, Neale Analysis of Reading Ability, Vernon spelling test, non-word reading and spelling and Word-Finding Vocabulary Scale.
Results Mean scores on language and non-verbal tests are shown in Table 1 for control children and for language-impaired 8-year olds divided according to status at 5 ^/4 years. Scores on standardized tests for each subgroup in Table 1 were compared to mean values from normative data using one-way analyses of variance. For non-standardized tests, scores of experimental groups were compared with the control group mean using one way analysis of variance. All F-ratios were significant at the 0.01 level. The general delay group differed significantly from control values on all tests, verbal and nonverbal. The children with poor outcome at 5 years scored significantly below control values on all verbal assessments except for Vernon spelling, where the difference fell just short of statistical significance. The mean score of this group on the non-verbal block design test was significantly below the norm, but the picture completion score was not. Children with good outcome at 5 years did not differ from normal controls except on two comprehension tests, TROG and WISC-R verbal comprehension, where mean scores were significantly below those of the standardization samples. Reading ability relative to intellectual level
It can be seen from Table 1 that children with poor outcome at 5 years and those
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D. V. M. Bishop and C. Adams
Table 1. Mean (S.D.) scaled scores on language tests at 8 ^ years Control 30)
Age (months)
100.5
(2.94)
100.0*^ 99.9^ 97 9'* 100.5 97.9 94.1
(14.9) (14.9) (16.6) (15.1) (18.7) (16.9)
Good outcome at 5 years (^ = 29) 99.9 96.5 92.0'' 91.7 " 105.1 98.5 100.4 105.2 102.0 96.4 105.0 101.7
BPVS TROG Verbad comprehension Word-finding
MLU Expressive semantics Reading accuracy Reading comprehension Spelling Block design Picture completion
98.7 (13.5)
"Significantly below control/normative value, '^Used as basis for computing scaled scores.
(0.86) (11.8) (13.0) (16.3) (11.2) (17.4) (17.2) (12.3) (12.6) (21.3) (12.4) (12.4)
Poor outcome at 5 years (A^=37)
General delay (A^= 16)
100.1 (1.35) 83.6"(13.6) 81.1" (9.4) 78.1" (12.2) 83.5" (16.3) 85.0" (18.4) 77.8" (17.9) 89.0" (14.6) 84.0" (14.9) 83.0 (12.8) 91.5" (17.2) 94.1 (11.6)
99.8 (1.24) 76.1"(15.2) 74.8" (7.8) 72.5" (12.2) 73.0" (19.0) 78.6" (19.0) 64.3" (12.7) 80.2" (20.2) 72.6" (18.6) 77.5" (12.4) 87.5"(25.7) 85.9" (12.6)
p u
120-
re u u re
10080-
re
6040 40
60
80
100
120
140
160
block design •«• picture completion
Fig. 1. Scatterplot showing relationship between non-verbal ability and reading accuracy at 8}-^ years for the language-delayed group. The regression hnes for control and language-delayed groups are also shown: the control line is the higher one. Both non-verbal ability and reading ability are shown as scaled scores with a mean of 100 and S.D. of 15. (D) Good outcome at 5 years; ( B ) poor outcome at 5 years; (A) general delay.
1033
Language impairment and reading retardation
reading accuracy from non-verbal ability for these two groups, with the languagedelayed group coded according to 5}/2-year old status. Neither the slopes nor the intercepts of these lines differed significantly. For reading accuracy, the adjusted scaled scores were 99.45 for the controls and 97.05 for the language-delayed sample. A different picture was obtained when reading comprehension scores were considered. Regression lines for control and language-delayed children are shown in Fig. 2, together with data points for individual children in the language-delayed sample. Slopes of the two lines did not differ significantly, but the intercepts were significantly different [F(l, 230) = 6.6; /)< 0.05]. The adjusted mean reading comprehension score for the control group was 99.39, and for the language-delayed group, 92.54. I4U -
o "w a> a>
D
120-
c CO
°
^
^
•
100-
D •
uo
•
••
-X"^ •
80-
4040
A
•
1 BA •• • • AAD •
•
60-
jJ2P;jcf^°D
• • •
A
AA
A
•
A 1
60
1
80
1
100
1
1
120
140
160
block design + picture completion
Fig. 2. Scatterplot showing relationship between non-verbal ability and reading comprehension at 8'/2 years for language-delayed group. The regression lines for control and language-delayed groups are also shown: the control line is the higher one. Both non-verbal ability and reading ability are shown as scaled scores with a mean of 100 and S.D. of 15. (CH) Good outcome at 5 years; ( H ) poor outcome at 5 years; (A) general delay.
These results suggest that children in the language-delayed group obtain reading comprehension scores that are disproportionately poor relative to their reading accuracy. A further analysis of covariance confirmed this impression: reading comprehension scores of language-delayed and control groups were compared after adjusting for reading accuracy. The effect of group was highly significant \F (1, 230) = 26.31; Thus when non-verbal ability is taken into account, the language-delayed group does not differ from the control group on reading accuracy, but is impaired on reading comprehension. The next question to ask is whether this deficit in comprehension is specific to written language, or whether it is one aspect of more general verbal impairment. It was noted above that the language-delayed children tended to do poorly on WISC-R verbal comprehension. To see how far poor reading scores could be explained in terms of this, a further analysis of covariance was carried out, this time adjusting reading scores relative to verbal as well as non-verbal ability, by using the summed scaled scores of all three WISC-R subtests (block design, picture completion
1034
D. V. M. Bishop and C. Adams
aind verbal comprehension) as covariate. There was no significant effect of group for either reading accuracy [F(l, 230) < l] or reading comprehension [F(l, 230) = 1.57]. We may conclude that the poor reading comprehension scores obtained by the language-delayed group can be explained in terms of their generally poor level of language understanding. Ability to read and spell non-words
Although the reading accuracy scores were very similar for those with good outcome at 5 years and the control group, it could be that the two groups were using different strategies to read. In particular, we were interested in the possibility that the children with a history of SLI might have difficulty learning phonics and so might rely more heavily on learning whole orthographic patterns, in which case they should be especially poor at non-word reading. Non-word error data are shown in Table 2. A logarithmic transformation was applied to non-word error data to stabilize variances, and a twoway analysis of variance used to compare the control group with the three subgroups of language-delayed children, treating non-word reading/spelling as a repeated measure. There was a highly significant main effect of group {F = 10.96; d.f. = 3, 108; p < 0.01) and of read/speU (F = 22.31; d.f = 1, 108; p < 0.01), but the interaction was not significant. The overall score of children with poor outcome at 5 years and those with general delay was significantly below that of control children and the group with good outcome at 5 years, who did not differ significantly from one another. Table 2. Mean (S.D.) phoneme errors (out of 25) in reading and spelling non-words
(A^=30)
Good outcome at 5 years (^ = 29)
Poor outcome at 5 years (A^=37)
General delay (N= 16)
7.7 (7.79)
5.3 (5.87)
12.3 (7.0)
16.1 (9.45)
5.7 (6.38)
3.4 (3.84)
8.1 (6.14)
16.3 (10.27)
Control
Non-word reading Non-word spelling
The scatterplot relating Neale reading accuracy to non-word reading errors is shown in Fig. 3. If the experimental group had disproportionate difficulty with non-word processing, their scores should cluster below the control regression line. It is clear from inspection that this is not the case. An analysis of covariance confirmed that neither the slopes nor the intercepts of the regression lines for predicting non-word errors from reading accuracy differed between control and language-delayed groups (all F-ratios< 1). How many children are reading retarded?
The above analyses make it clear that the numbers of children classified as reading retarded will depend crucially on the definition adopted. Although not all authors accept this procedure (e.g. Siegel, 1988), it is common for a distinction to be drawn between those children whose low reading attainments
1035
Language impairment and reading retardation
>u a
(0
'•3
-2 o o
40
60
80
100
120
140
Neale reading accuracy (scaled)
Fig. 3. Scatterplot showing relationship between Neale reading accuracy and non-word reading accuracy. The plotted line is the regression of non-word reading on reading accuracy for controls. ( x ) Control; (D) good outcome at 5 years; ( I ) poor outcome at 5 years; (A) general delay.
are compatible with their limited intelligence, and those poor readers of normal intelligence. Yule and Rutter (1976) have recommended defining specific reading retardation (SRR) in terms of the regression equation relating reading ability to I.Q. A child whose reading score is significantly below the level predicted from I.Q. is regarded as specific2dly reading retarded, whereas one whose reading is poor but consistent with I.Q. is termed a 'backward reader'. Using the control regression lines relating non-verbal ability to reading accuracy and comprehension (see Figs 1 and 2), children in the language-delayed sample were categorized as follows. SRR: A—specific reading retarded on accuracy: this group consisted of children whose obtained reading accuracy was more than 1.96 S.D.s below the value predicted from their summed block design and picture completion scores. SRR:C—specific reading retarded on comprehension: these were children whose obtained reading comprehension was more than 1.96 S.D.s below the value predicted from their summed block design and picture completion scores. BR—backward readers: these were children whose reading scaled score was below 71 on either scale, but who did not fall into either SRR group. (In Bishop and Butterworth's normal sample, 3% of children fell into this category.) All those who did not fit the criteria for one of these categories were classed together as normal readers. Note that the two categories of SRR are not mutually exclusive. Five children met the criteria for both SRR: A and SRR:C. Two of these had poor outcome at 5 years and three were from the general delay group. Two children (both with poor outcome at 5 years) were included in the category SRR:A but not SRR:C, and five children (one good outcome at 5 years, one poor outcome at 5 years, and three general delay) met criteria for SRR:C but not SRR:A. Overall, seven out of 82 children (8%) met
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D. V. M. Bishop and C. Adams
criteria for SRR:A, and 10 (12%) met criteria for SRR:C. In the general population we would predict that 5% of children should fall in each category. The frequency of SRR:A is not significantly different from expectation (chi-square with Yates' correction = 1.48, d.f = 1), but the frequency of SRR:C is significantly above expectation (chi-square = 7.49, d.f. = 1, p
