1 Reading Development in Children with SLI. Growth of Reading Skills in Children with a History of Specific Language

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1 1 Reading Development in Children with SLI Running head: Reading Development in Children with SLI Growth of Reading Skills in Children with a History of Specific Language Impairment (SLI): The Role of Autistic Symptomatology and Language Related Abilities Michelle C. St. Clair 1, Kevin Durkin 2, Gina Conti-Ramsden 1, Andrew Pickles 1 1 The University of Manchester, Manchester, UK 2 University of Strathclyde, Glasgow, UK Corresponding author: Professor Gina Conti-Ramsden Division of Human Communication and Deafness School of Psychological Sciences Ellen Wilkinson Building The University of Manchester Oxford Road Manchester, UK M13 9PL gina.conti-ramsden@manchester.ac.uk Acknowledgements The authors acknowledge the Economic and Social Research Council Fellowship (RES ) awarded to Gina Conti-Ramsden. We also acknowledge the support of the Nuffield Foundation for grant numbers AT251 [OD], DIR/28, EDU 8366 and EDU 32083, and the Wellcome Trust for grant which supported the data collection. The authors also thank the research assistants for their help in data collection and Zoë Simkin for aiding and assisting in the data organisation.

2 2 Reading Development in Children with SLI Abstract Individuals with a history of specific language impairment (SLI) often have subsequent problems with reading skills, but there have been some discrepant findings as to the developmental time course of these skills. This study investigates the developmental trajectories of reading skills over a nine year time span (from 7 to 16 years of age) in a large sample of individuals with a history of SLI. Relationships among reading skills, autistic symptomatology and language related abilities were also investigated. The results indicate that both reading accuracy and reading comprehension are deficient but that the development of these skills progresses in a consistently parallel fashion to what would be expected from a normative sample of same age peers. Language related abilities were strongly associated with reading skills. Unlike individuals with SLI-only, those with SLI and additional autistic symptomatology had adequate reading accuracy but did not differ from the individuals with SLI-only in reading comprehension. They exhibited a significant gap between what they could read and what they could understand when reading. These findings provide strong evidence that individuals with SLI experience continued, long-term deficits in reading skills from childhood to adolescence.

3 3 Reading Development in Children with SLI Growth of Reading Skills in Children with a History of Specific Language Impairment (SLI): The Role Autistic Symptomatology and Language Related Abilities Academic problems in children with specific language impairment (SLI) have long been observed, but perhaps the most consistent finding is problems with reading. This is true both of children who continue to demonstrate overt difficulties with language and those whose language problems resolve (Bishop & Adams, 1990; Simkin & Conti-Ramsden, 2006; Stothard, Snowling, Bishop, Chipchase, & Kaplan, 1998). Indeed, it has been found that reading difficulties are present at a higher rate than other academic difficulties in children who have a history of SLI (King, Jones, & Lasky, 1982). This study focuses on the longitudinal development of reading skills in individuals with a history of SLI. Both reading accuracy and reading comprehension are examined as well as the role of autistic symptomatology and language related abilities in reading development. Theoretical Models of Poor Reading Developmental studies have shown that reading ability develops nonlinearly, exhibiting more rapid growth in childhood followed by a slowing down, i.e., plateau, in the rate of learning during adolescence (Francis, Shaywitz, Stuebing, Shaywitz, & Fletcher, 1996). With this evidence in mind, several theories have attempted to characterize the developmental growth of reading skills between good and poor readers. The deficit model of reading (Cromer, 1970; Francis et al., 1996) suggests that reading difficulties are due to problems with a necessary skill or skills that never develop appropriately; therefore the pattern of growth is characterised by initial lower levels of reading ability which then appear to follow the same developmental trajectory of growth as found in typically developing (TD) individuals. Children with

4 4 Reading Development in Children with SLI reading difficulties develop in parallel to TD children and are always deficient when compared to age-matched peers. In contrast, the developmental lag model of reading development assumes that reading difficulties are due to underlying delays in cognitive skills which eventually reach age appropriate level (i.e., vocabulary, phonological skills, decoding and word-naming abilities). This model predicts, therefore, that children with reading difficulties will differ primarily in early reading ability and eventually reach age typical reading skills through the late but accelerated growth in the underlying cognitive skills upon which reading replies (Fletcher, 1981; Satz, Taylor, Friel, & Fletcher, 1978; Stanovich, Nathan, & Zolman, 1988). Another model, the slower growth model, postulates Matthew effects in children with reading difficulties, such that the initial lower reading ability will result in slower developmental growth in reading, based on the reduced amount of reading exposure in these children. Thus, children with reading difficulties will have initial lower reading abilities and slower growth than typical children. The gap between those with reading difficulties and their TD peers increases as the children develop, although both groups reach a plateau in adolescence (Stanovich, 1986). Thus, in respect of children who manifest early reading difficulties, the deficit model predicts relatively poor reading ability throughout development whilst the developmental lag model predicts an eventual increase (catching up) in reading ability. The slower growth model predicts that progress will be inhibited in those with early difficulties, and that the gap between them and good readers will widen over time. In general, data from children with reading disabilities point to reading ability developing in a parallel fashion but at a lower overall level when compared to TD children, thus supporting the deficit model (Francis et al., 1996). Early studies found initial support for the developmental lag hypothesis. Children with reading difficulties

5 5 Reading Development in Children with SLI appeared to develop at a faster rate than TD children in that they caught up in cognitive skills strongly predictive of reading ability. This is consistent with regression to the mean. However, these studies did not find that the strengthening of cognitive skills throughout development led to equivalent reading ability between groups (Satz et al., 1978; Stanovich et al., 1988). In the same vein, though early evidence pointed to Matthew effects in reading (for a review see Stanovich, 1986), later longitudinal studies did not find evidence consistent with slower growth in comparison to TD children (Francis et al., 1996; Shaywitz et al., 1995). The Development of Reading Skills in Children with SLI How reading skills develop in children with SLI has received less research attention. It has been argued that they may follow a different developmental trajectory, given the fact that language abilities underpin reading skills (Catts, 1993; NICHD Early Child Care Research Network, 2005; Storch & Whitehurst, 2002). There is certainly evidence, from a range of studies, that children with a history of SLI have difficulties with both reading accuracy (Catts, 1993; Catts, Bridges, Little, & Tomblin, 2008; Catts, Fey, Tomblin, & Zhang, 2002; Huntley, Holt, Butterfill, & Latham, 1988; Magnusson & Nauclér, 1990; Simkin & Conti-Ramsden, 2006; Snowling, Bishop, & Stothard, 2000) and reading comprehension (Bishop & Adams, 1990; Catts, 1993; Catts et al., 2008; Catts et al., 2002; Huntley et al., 1988; Simkin & Conti-Ramsden, 2006; Stark et al., 1984). Tomblin, Zhang, Buckwalter and Catts (2000) found a substantial overlap between SLI and reading disorders. Approximately half the children with SLI appeared to have difficulties learning to read (46% for reading accuracy and 52% for reading comprehension), while the corresponding rate for reading disorders in the TD comparison group was 9%. Most of this evidence,

6 6 Reading Development in Children with SLI however, pertains to between-group differences rather than the course of development over time. In an early study examining the development of both reading accuracy and comprehension, Bishop and Adams (1990) investigated a sample of 83 children who were initially diagnosed as having SLI at age 4 and followed their development at 5 and 8 years of age. At age 8, the reading comprehension skills of the children with SLI were impaired relative to the control sample, but this was not the case for reading accuracy. Bishop and Adams concluded that this deficit in reading comprehension was accounted for by a lower level of language comprehension in general. These authors also found that in terms of patterns of impairment in children with SLI, the occurrence of difficulties in reading accuracy was not above the level expected in the normal population, but the occurrence of difficulties in reading comprehension was above expected levels. In further analyses, Bishop and Adams (1990) split their sample according to language outcome at age 5 (resolved SLI, persistent SLI, and generally delayed). They found that the resolved SLI group did not differ from the TD comparison group in terms of errors in reading and spelling nonwords. Furthermore, 96% of the resolved group were labelled as normal readers at age 8. The groups classified as persistent SLI and general delay made significantly more errors on the nonword reading and spelling tasks and had a larger proportion of poor readers. Thus, it appears that SLI which resolves in early childhood is related to a reduced risk for reading problems in later childhood, whereas there is a higher likelihood of problems if the language difficulty persists. Stothard et al. (1998) re-examined 71 of the Bishop and Adams (1990) sample when the children were age 15. In terms of literacy difficulties, the resolved group

7 7 Reading Development in Children with SLI showed impairments, relative to the TD comparison group, in an overall composite of reading accuracy, comprehension and spelling abilities. Nevertheless, these literacy skills were within the normal range (within 1 SD below the mean). The literacy abilities of the persistent SLI and general delay groups were similar to each other, both performing at about 2 SDs below the comparison group. The results at age 15 mirror the age 8 results in that children with persistent language difficulties had poorer reading outcomes. However, when the data for reading accuracy and reading comprehension were examined separately for the sample (excluding those with general delay only), results revealed that 43% of the participants now had reading accuracy difficulties (Snowling et al., 2000). This suggests that there had been a slowing down in the development of reading accuracy skills in individuals with SLI between the ages of 8 and 15 years relative to their TD peers. Catts et al. (2002) examined a sample of 208 children with SLI at age 6 and retested them at ages 8 and 10. The children with preschool SLI appeared to be developing in parallel with same-age TD peers, simply at a lower overall reading level. This result provides support for the deficit model of reading development, at least up to middle childhood. Catts et al. (2008) further investigated this sample and expanded the time frame by including measures at ages 14 and 16. Support for the deficit model of reading growth obtained again across this longer span. The developmental trajectories for both reading accuracy and reading comprehension showed equivalent growth patterns in both the SLI group and the TD comparison group. However, at each time point, the SLI group was at a lower overall level than the same age TD group. At present, most of the available data across early to middle childhood for individuals with SLI support the deficit model. The evidence is more mixed for the

8 8 Reading Development in Children with SLI period of adolescence, with some studies suggesting slower growth and a widening gap (Snowling et al., 2000), whilst others illustrating a steady deficit (Catts et al., 2008). There is therefore a need for further evidence, in particular with regard to the period leading up to and including adolescence. In this investigation, we examine the growth trajectories of reading abilities in a large sample of individuals with a history of SLI, spanning a nine year developmental period from childhood (7 years) to adolescence (16 years). It is important to note that SLI is a heterogeneous condition (Conti-Ramsden, 2008). Although attempts at sub-classifications of SLI have had limited success (Bishop, 1994; Conti-Ramsden & Botting, 1999b; Conti-Ramsden, Crutchley, & Botting, 1997; Rapin, 1996; Rapin & Allen, 1987), it is clear that SLI includes a variety of profiles of impairment. Two main aspects of SLI appear particularly relevant to the study of reading skills: the degree of impairment of language related abilities and the presence/absence of autistic symptomatology. Language Related Abilities and Reading Skills Distinct cognitive skills underlie the ability to read the written word and also to comprehend what has been read. When investigating individuals with dyslexia, specific deficits in the phonological representation of language have been identified. Poor phonological skills are likely to cause difficulties translating orthography to phonology resulting in poor reading accuracy that characterises dyslexia (Hulme & Snowling, 2009). Individuals with dyslexia have poor phonological awareness (or the ability to explicitly recognise and break apart the phonemic units of language) as well as impaired phonological processing (or the implicit ability to process phonological material). However, individuals with dyslexia also have been shown to have subtle difficulties in early language ability, such as problems with pronunciation, receptive

9 9 Reading Development in Children with SLI vocabulary, object naming, verbal short term memory, and phonological awareness (Scarborough, 1990). These oral skills are not thought to be directly related to the reading difficulties observed in dyslexia, but rather may have their influence on reading skills via a mediating effect of phonological deficits (for a review see Hulme & Snowling, 2009). Specific problems in reading comprehension in the context of normal reading accuracy are not characterised by deficits in the phonological system. Instead, poor comprehenders generally have more severe language problems, and a substantial minority of these children appear to meet criteria for SLI when tested, though they usually have not been previously identified (Nation, Clarke, Marshall, & Durand, 2004). Poor comprehenders have difficulties using the grammatical structure of the text to make inferences about the semantic content. They also have attention problems and thus experience difficulties in discarding irrelevant information. Comprehension monitoring is impaired in these individuals. Generally, poor comprehenders are characterised by fundamental weaknesses in semantic processing, which are combined with poorer comprehension monitoring and difficulty suppressing irrelevant material, thus delaying the processing of relevant and necessary detail in order for sufficient comprehension (Hulme & Snowling, 2009). These underlying cognitive weaknesses cause a number of oral language difficulties, reflected in impaired narrative skills, receptive language, and vocabulary development, as well as poor comprehension of text. Supporting the findings with poor comprehenders, research with large samples of TD children has linked expressive language abilities, such as oral vocabulary and narrative skills, to early reading comprehension abilities (NICHD Early Child Care Research Network, 2005; Roth, Speece, & Cooper, 2002). Other studies have found

10 10 Reading Development in Children with SLI similar relationships. Storch and Whitehurst (2002) revealed that oral language skills (naming vocabulary) throughout the early reading years were related to later reading comprehension at ages 8 to 10. However, in this same longitudinal study, reading accuracy at ages 8 to 10 years was predicted by earlier reading ability and phonological skills; oral language skills did not seem to influence early reading accuracy ability. These studies support the view that broader language skills relate to reading comprehension whilst specific phonological skills relate to reading accuracy. With regard to children with SLI, problems in both reading accuracy and reading comprehension are expected. Deficits in phonological memory, as indexed by nonword repetition problems, have been found consistently in individuals with SLI (Conti-Ramsden & Durkin, 2007). Thus, problems in phonological processing are likely to predict difficulties in reading accuracy. In terms of reading comprehension, it is interesting to note that the language skills linked to reading comprehension abilities are similar in nature to the fundamental language difficulties found in children with SLI. Additionally, the general cognitive capacity limitations and attentional allocation difficulties that are often found in individuals with SLI (Miller, Kail, Leonard, & Tomblin, 2001; Montgomery & Evans, 2009) are likely to make reading comprehension a particular area of weakness in SLI. These skills have been found to be important in the integration of relevant details crucial in understanding narratives (Montgomery, Polunkenko, & Marinellie, 2009). Catts (1993) found that measures of phonological skills in children with SLI aged 5 to 6 years explained much of the variance in reading accuracy two years later, whereas early expressive and receptive language abilities were the main predictors in explaining the variance in later reading comprehension ability (also see Catts et al., 2002, for similar results). Similarly, Botting, Simkin and Conti-Ramsden (2006) found that receptive language skills at 7

11 11 Reading Development in Children with SLI years significantly predicted reading comprehension abilities at age 11 years and that reading comprehension was generally more impaired than reading accuracy. Further work with this sample suggested that the effect of language ability on reading outcomes is likely to be continuous whereby poorer language abilities lead to poorer reading outcomes (Simkin & Conti-Ramsden, 2006). However, most studies have focused mainly on the emergence or early development of reading abilities up to middle childhood (i.e., Botting et al., 2006; Roth et al., 2002). Little information is available regarding the nature of these relationships during adolescence and whether different subgroups of individuals with SLI exhibit different patterns of relationships. Autistic Symptomatology and Reading Skills Autistic symptomatology within the context of SLI has received recent attention. Conti-Ramsden, Simkin and Botting (2006) found a subgroup of individuals in their sample with SLI who met criteria for a mild, broad autism phenotype in adolescence. These children exhibited autistic symptomatology, though insufficient to warrant a full diagnosis of autism (Risi et al., 2006). Individuals in this subgroup are referred to as having SLI with autistic symptomatology (SLI+ASD). Within this context, what may be expected of the reading skills of individuals with SLI and autistic symptomatology? Research with individuals with autism spectrum disorders (ASD) suggests that the reading development of the SLI + ASD group should provide particularly useful evidence towards disentangling the relationships among language and reading abilities It is known that the pattern of reading skills in individuals with ASD often involves good (sometimes even exceptionally good) reading accuracy skills, coupled with impaired reading comprehension skills (Minshew, Goldstein, Taylor, & Siegel,

12 12 Reading Development in Children with SLI 1994; Nation, Clarke, Wright, & Williams, 2006). In other words, these two component reading skills tend to be out of step with each other. Nation et al. (2006) also found that language skills were related to reading comprehension, such that less skilled comprehenders had lower receptive vocabulary and oral comprehension skills (see also Snowling & Frith, 1986 for similar results). Additionally, these authors found that individuals with ASD had high levels of reading accuracy even in the context of poor reading comprehension. These authors did not measure phonological skills in their study. However, children with ASD have been found to have better phonological memory than children with SLI (Botting & Conti-Ramsden, 2003). Their reading accuracy skills have also been found to be related to phonological abilities (Frith & Snowling, 1983). Taken together, this evidence suggests that increased phonological abilities may play a role in the stronger reading accuracy skills found in individuals with ASD when compared to individuals with SLI. Thus, it would be of interest to examine whether the above pattern of reading abilities prevails in individuals with SLI who also exhibit autistic symptomatology during adolescence. Furthermore, given the mixed findings for the growth trajectories of reading skills in individuals with SLI (Catts et al., 2008; Snowling et al., 2000) it would also be of interest to examine the relationship between language related abilities (phonological memory, expressive and receptive language) and reading skills in this subgroup in order to provide insights into potential sources of variation. The Present Study This study aims to expand our understanding of the reading skills of individuals with a history of SLI by taking a longitudinal perspective over a nine year time span and investigating relationships with autistic symptomatology and language related abilities. Three areas formed the specific focus of this investigation.

13 13 Reading Development in Children with SLI First, to facilitate comparisons with previous research, we examine the developmental trajectories of reading skills (accuracy and comprehension) in the entire sample of individuals with a history of SLI in our study, from age 7 to 16 years. We use two methods in this analysis. On the one hand, we examine the trajectories using a common metric that allows us to evaluate individuals growth across the developmental period examined. On the other hand, we examine the trajectories using standard scores to allow an evaluation of individuals performance in relation to what would be expected of a normative sample of their same age peers. This strategy enables us to distinguish between intra-individual development, (examining to what extent the participants improve relative to their own early performance), and development relative to typical peer progress (examining whether gaps decrease, remain constant, or increase over time). Second, we investigate whether the presence or absence of autistic symptomatology influence a) the developmental trajectories of reading skills in the nine year period and b) the pattern of reading skills observed. Third, we analyse the relationship between language related abilities (phonological memory, expressive and receptive language) and reading skills in individuals with SLI with and without autistic symptomatology. Method Participants Children with a History of SLI The participants with a history of SLI in this investigation were part of a longitudinal study: the Conti-Ramsden Manchester Language Study (Conti-Ramsden & Botting, 1999a, 1999b; Conti-Ramsden et al., 1997). The initial study cohort included in this paper was 239 children, aged 6;5 years to 7;9 years, of which 183

14 14 Reading Development in Children with SLI were males and 56 (23.1%) females. These children were reassessed as part of the original study at 8 (n = 227), 11 (n = 199), 14 (n = 112, this decline in numbers was due to the project funding a proportion of the original cohort only) and 16 (n = 44) years of age. See Table 1 for details of the sample size at each time point. None of the participants with a history of SLI were administered the psychometric tests of interest to this study at both 14 and 16 years of age, which accounts for the low numbers at age 16. This sample is used for all analyses, unless the subgroups defined below are specified. Performance IQ (PIQ) at age 7 (Coloured Progressive Matrices; Raven, 1986) was found to be in the normal range, M = , SD = The effect of PIQ on reading accuracy and comprehension was assessed using a mixed model regression (used throughout all longitudinal analyses; fully described below). For reading accuracy, PIQ at age 7 was a significant fixed effect, β =.31, CI =.20 to.41, p <.001. PIQ at age 7 was also a significant fixed effect on reading comprehension, β =.36, CI =.24 to.48, p <.001. Therefore, in the following analyses, PIQ at age 7 was included as a covariate. There was a significant difference in reading accuracy and between male and female participants, β = 4.84, CI = 1.19 to 8.49, p <.01, with female participants having slightly higher reading accuracy ability than male participants, M = 84.03, SD = for females and M = 81.83, SD = for males. There was no difference between the genders for reading comprehension, β = 3.14, CI = -.81 to 7.10, p >.10. When investigating parental income at age 16 (< 10,401, 10,401-20,800, 20,801-36,400, and > 36,400; at income levels), there were no differences in reading accuracy or comprehension between the differing levels of parental income, ps >.30 for reading accuracy and ps >.02 for reading comprehension (significance

15 15 Reading Development in Children with SLI level set at.01). Similarly, there was no difference in maternal education at age 16 (no qualification, basic educational qualification [GCSE/O-level to some college education] and higher education [university degree/postgraduate]) in either reading accuracy or reading comprehension, ps >.10 and ps >.02, respectively. -Table 1 about here- Subgroup of Children with Autistic Symptomatology It has been previously found that there is a subgroup of children with SLI in this sample that displays autistic symptomatology (Conti-Ramsden et al., 2006). At age 14 the Autism Diagnosis Interview-Revised (ADI-R; Lord, Rutter, & Le Couteur, 1994) and the Autism Diagnostic Observation Schedule (ADOS; Lord, Rutter, DiLavore, & Risi, 1999) were administered. Five young people were diagnosed with autism by both of these gold standard autism diagnosis instruments and thus met criteria for full autism (Conti-Ramsden et al., 2006). It is a matter of debate whether these individuals represent misdiagnosed cases of autism or true cases of late-onset autism in SLI (where autistic symptoms develop outside the typical age range for autism diagnosis). However, in order to be conservative we did not include them in this analysis. A further 28 children showed some evidence of broad phenotype autistic behaviours, i.e. autistic symptomatology without full diagnosis. These children either met criteria for ASD on the ADOS (that focuses on current researcher observation) or achieved impairment level in the social domain of the ADI-R (that focuses on symptoms during the 4-5 age period) in addition to impairment level on at least one of the remaining two domains (communication or repetitive/stereotyped behaviours), or qualified on both criteria (Risi et al., 2006). A total of nine children qualified for ASD status by the results of the ADOS alone, indicating only current, but not historic symptoms, while 10 qualified only on

16 16 Reading Development in Children with SLI the ADI-R historical symptoms. The remaining nine qualified for ASD status through both the ADI-R and ADOS criteria, but their symptoms were not enough to meet criteria for full diagnosis. Thus, the majority of the individuals in this subgroup (68%) had some historic symptoms. We are aware that the issues relating to classification and diagnosis of these individuals are also complex. Nonetheless, for the purposes of this investigation, we refer to the aforementioned 28 children as SLI+ASD, whereas the remainder of the children (56) who did not meet criteria for ASD are referred to as SLI-only. See Table 1 for details of the subgroup sample size at each time point. Given the potential influence of underlying cognitive skills on reading abilities, we examined PIQ and processing speed across the two subgroups (Hulme & Snowling, 2009; Miller et al., 2001; Montgomery et al., 2009). PIQ at age 7 did not differ between the two subgroups, β = 6.24, CI = to 13.57, p =.09, M = , SD = for the SLI+ASD subgroup and M = , SD = for the SLI-only subgroup. There was no difference in processing speed at age 14 between the two subgroups, β = 2.05, CI = -.69 to 4.78, p =.14, M = 13.00, SD = 6.04 for the SLI+ASD subgroup and M = 16.14, SD = 6.20 for the SLI-only subgroup. Finally, all of the children in the SLI-only and SLI+ASD subgroups were tested at age 14. Thus, the longitudinal trends for these subgroups extends to that age only, as these psychometric tests were not repeated at age 16 if the children had already been tested at age 14. Measures There were three types of psychometric tests administered to this sample that formed the focus of this study: measures of reading, measures of language skills and performance IQ. Reading

17 17 Reading Development in Children with SLI Reading accuracy was measured at ages 7, 8, 11, 14 and 16. Reading comprehension was measured at ages 11, 14 and 16 only. Reading accuracy. At ages 7 and 8, the word reading subtest of the British Abilities Scale (BAS; Elliot, 1983) was administered. At ages 11, 14 and 16 the basic reading subtest of the Wechsler Objective Reading Dimensions (WORD; Wechsler, 1993) scale was utilised. Both of these measures of reading accuracy comprised single word reading. A series of printed words were presented to the participants and they were encouraged to read as many as they could in the order specified on the cards. The words became progressively more difficult. The WORD subtest differed from the BAS in that only ten words were presented at once, whereas the BAS presented all words on one card to the children. Additionally, the BAS did not have a time restriction for responses, whereas the WORD specified a ten second time limit. However, children rarely failed to respond during this limit unless they did not know the word. Due to the general similarity and minimal differences between the two tests, they are often combined in the analyses reported below. The BAS word reading score for each participant was converted to a percentile ranking based on the published norms. This percentile rank was converted to a standard score (with a mean of 100 and standard deviation of 15). The norms for the WORD reading subtest were in terms of standard scores. Reading comprehension. The reading comprehension subtest of the WORD was administered at age 11, 14 and 16. The children had to read printed passages of varying lengths. After reading the passage the child was asked a question relating to it. The examiner recorded the child s response verbatim on the response sheet and the responses were later scored as correct or incorrect.

18 18 Reading Development in Children with SLI Language Related Skills These skills were only investigated at age 14. Phonological memory was examined using the Nonword Memory Test (Gathercole & Baddeley, 1996). This test consists of 28 nonwords of various length and complexity which young people repeat after presentation. Standard scores were derived from a normative sample (Gathercole & Baddeley, 1996). The Clinical Evaluation of Language Fundamentals-Revised (CELF-R; Semel, Wiig, & Secord, 1987) receptive and expressive language scores were the oral language measures. Both of these language scores were composed of three subtests, which combined give a measure of language expression and language understanding. PIQ Raven s Coloured Progressive Matrices (Raven, 1986) was used at age 7 as a measure of the participants PIQ. This test presents the child with a series of patterns in which a piece of the pattern is missing. The task entails studying the pattern and choosing from six alternative pieces which one completes the pattern. Processing speed at age 14 was measured by the Wechsler Intelligence Scale for Children (WISC-III UK; Wechsler, 1992). Statistical Analyses All longitudinal data were analysed with multilevel mixed-effects linear regression using maximum likelihood. This accounts for the non-independence of repeated measures data and for selective attrition (e.g. that associated with declining previous scores) on the assumption that the missing data mechanism is missing at random (Rubin, 1976). Within the fixed-effects, models explored both structured linear and quadratic trends in age, and unstructured patterns in which age was treated categorically. The significance and 95% confidence intervals of trends and age-

19 19 Reading Development in Children with SLI contrasts were estimated using standard errors from the estimated parameter covariance matrix. The models included random intercepts and for reading accuracy a random slope to account for the variation in variance evident between age 7 and 8 BAS and age 11 and 14/16 WORD tests. PIQ at age 7 was included as a covariate in all analyses to control for the independent effect of PIQ on reading skills. Gender was added as a covariate to the reading accuracy analyses only, as gender had an independent effect on reading accuracy, but not comprehension. To control for multiple comparisons, the significance level was set to the.01 level (p <.01). However, for interest, we report results as marginal when alpha varied between 0.01 and All statistical analyses were conducted within Stata SE, version 10.1 (Stata SE, 2008). All graphs were also created within Stata SE with fitted values from the mixed effects regressions described above. Fitted values were used for the graphs instead of the raw data as the fitted values accounted for participant attrition across the 9 year time span as well as differences in PIQ. However, unadjusted participant data (not fitted values) was used when reporting the means and standard deviations. Correlation coefficients between two subgroups of SLI individuals were directly compared to each other using a procedure of transforming the r statistic to a z score. The two z scores were then directly compared to determine whether they were significantly different from each other using the procedure outlined by Edwards (1984). An effect size, q, was calculated for the test of correlation coefficients as outlined by Cohen (1988). For analyses comparing subgroups on receptive and expressive language measures, correction was made for the presence of a floor effect in the distribution of test scores by the use of interval regression analysis in place of simple difference of mean t-tests.

20 20 Reading Development in Children with SLI Results Developmental Trajectories of Reading Skills In order to determine the developmental trajectories of reading accuracy and reading comprehension of individuals with SLI, two methods were used. In the first method, all scores from ages 7, 8, 14 and 16 were scaled to standard scores based on norms appropriate for age 11 children. The age 11 time period was selected as it contained the most commonly used measure (WORD) as well as being approximately in the middle of the range studied. Scaling was done by using the age appropriate standard scores for ages 7, 8, 14 and 16 to obtain the equivalent WORD raw score for the same standard score at the mean age for each time period. The WORD raw scores for ages 7, 8, 14 and 16 were then converted to age 11 standard scores. This scaling allowed us to put the variables of interest, i.e. reading accuracy and reading comprehension, on a common and therefore comparable metric. In the second method, all analyses were repeated using the original standard scores for each test used at each time point. This standard score analysis afforded the comparison of the group of individuals with SLI in relation to what would be expected from a normative sample of same age peers, for whom the mean is 100 and the standard deviation is 15. A mixed effects regression model was used to test linear and quadratic trends. If significant effects were found, a further analysis comparing each different age point as a categorical effect followed. Finally, correlational analyses were carried out, where appropriate, to measure the strength of the relationships across time. Reading Accuracy The analysis using the scaled scores revealed a highly positive linear trend, β = 8.50, CI = 7.20 to 9.80, p <.001, as well as a quadratic trend for the age variable, β = -.18, CI = -.24 to -.12, p <.001. The quadratic trend was due to a reduction in the

21 21 Reading Development in Children with SLI slope from age 14 to age 16, indicating a lack of growth in reading accuracy ability for that period. When analysed categorically, each age point was significantly different from each other, ps <.001, except ages 14 and 16, which did not differ from each other, β =.87, CI = to 4.26, p =.62. Table 2 presents the means and SD for each age point. These data reveal that there is growth in reading accuracy skills in individuals with SLI from childhood to early adolescence, with a reduction in rate of development during adolescence (see Figure 1). - Table 2 and Figure 1 about here- The analysis using standard scores revealed no significant linear or quadratic effects of age on the development of reading accuracy, β = -1.03, CI = to 0.29, p =.13 for the linear trend, and β =.05, CI = -.01 to.11, p =.13 for the quadratic trend. See Table 2 for descriptive statistics of the standard scores by age period. These data indicate that reading accuracy in individuals with SLI develops consistently in parallel to that expected from a normative sample of same age peers, but at approximately 1 SD below the expected standard score mean of 100, as can be seen in the right graph of Figure 1. Correlational analyses supported the above findings. There were significant, strong associations across time between reading accuracy scores (rs =.56 to.89, all ps <.001). Reading Comprehension The regression analysis using scaled scores revealed a significant linear and quadratic effect of age on reading comprehension skills, β = 28.33, CI = to 40.03, p <.001 for the linear effect and β = -.97, CI = to -.52, p <.001 for the quadratic effect. When tested categorically, it was found that ages 14 and 16 had higher reading accuracy scaled scores than age 11, β = 12.38, CI = to 14.44, p <.001 and β = 10.95, CI = 7.78 to 14.11, p <.001, respectively. However, ages 14 and

22 22 Reading Development in Children with SLI 16 did not differ from each other, β = -1.43, CI = to 2.20, p =.44. These data reveal that there is growth in reading comprehension skills in individuals with SLI from ages 11 to 14, but a plateau in growth during adolescence (see mean scores in Table 2). A similar regression was conducted using standard scores. There was no significant linear or quadratic trend in reading comprehension standard scores, ps >.09, indicating that (at least from age 11 onwards) reading comprehension in individuals with SLI develops in parallel to that expected from a normative sample of their same age peers, but at approximately 1.5 SD lower. Correlational analysis also supported these findings (rs =.72 to.74, all ps <.001). Autistic Symptomatology and Reading Skills Developmental Trajectories A similar approach as that described above for the whole group was used for the analysis of the SLI+ASD and SLI-only subgroups. Reading accuracy in SLI+ASD and SLI-only subgroups. When examining scaled scores, the age linear trends were highly significant for both the SLI+ASD and SLI-only subgroups, β = 5.28, CI = 4.55 to 6.01, p <.001 for the linear SLI+ASD trend and β = 4.60, CI = 4.11 to 5.10, p <.001 for the linear SLI-only trend. There were no significant quadratic trends, which is consistent with the previous result indicating linear growth in reading skills until early adolescence and a plateau of skills thereafter (see Figure 2). As we have no age 16 data, the plateau period is not evident in the current analysis. All time points differed significantly from each other when age was examined categorically in both subgroups, ps <.001, with increases in reading accuracy occurring as individuals develop. Table 3 presents the descriptive statistics for the two subgroups. - Table 3 and Figure 2 about here-

23 23 Reading Development in Children with SLI Next, the standard scores were compared across time. Beginning with the SLIonly subgroup, there were significant linear, β = -3.69, CI = to -1.04, p <.01, and quadratic age trends, β =.17, CI =.05 to.30, p <.01. The mean standard scores are given in Table 3. Categorical analysis revealed no significant or marginal differences in standard scores between the age points. The significant linear and quadratic trends are reflective of the slight decrease from age 7 and 8 to age 11 and then a slight increase to age 14 from age 11. However, the lack of differences between the age periods indicates that standard scores in reading accuracy are generally consistent over time in the SLI-only subgroup. The mean standard scores for the SLI+ASD subgroup showed the same pattern as the SLI-only subgroup (see Table 3). However, due to the relatively small number of participants there were no detectable linear effects, β =.42, CI = -.34 to 1.18, p =.28. Thus, both groups appeared to be developing in parallel to what would be expected of a normative sample of same age peers except that the SLI-only subgroup was functioning at around 1 SD below expectation whilst the SLI+ASD subgroup was functioning closer to typically developing peers, i.e. within 1 SD from the mean (see right graph of Figure 2). The associations in reading accuracy over time for both the SLI+ASD and SLI-only subgroups were then examined. As can be seen in Table 4, the correlations in reading accuracy across time were strong for both subgroups of individuals. - Table 4 about here - Reading comprehension in SLI+ASD and SLI-only subgroups. Similar analyses examined reading comprehension. The scaled score analysis revealed a significant linear effect for both the SLI+ASD and SLI-only subgroups, β = 3.96, CI = 2.65 to 5.28, p <.001 and β = 3.79, CI = 2.70 to 4.88, p <.001, respectively (see Table 3 for the means and SD). The analysis using standard scores

24 24 Reading Development in Children with SLI found no significant linear trend of age, β = -.09, CI = to.93, p =.85 for the SLI-only subgroup and β = -.10, CI = to 1.06, p = 87 for the SLI+ASD subgroup (see Table 3 for the means and SD). Overall these results indicate development that is parallel to a normative sample of same age peers, except that both subgroups were functioning at approximately 1.5 SD below expectation. When examining the correlations in reading comprehension between ages 11 and 14 for both the SLI+ASD and the SLI-only subgroups separately, significant, strong correlations were found for both groups (.87, p <.001 for the SLI+ASD subgroup and.56, p <.001 for the SLIonly subgroup). Interestingly, the correlation between reading comprehension at ages 11 and 14 was significantly higher in the SLI+ASD subgroup than in the SLI-only subgroup, z = 2.85, p <.005, q =.71 indicating that a significantly stronger relationship in reading comprehension across time is associated with autistic symptomatology. Reading Accuracy-Comprehension Discrepancy As can be seen from a visual inspection of Figure 2, there appears to be a difference in reading accuracy between the subgroups. Statistical analysis revealed that the SLI+ASD subgroup (M = 88.44, SD = 16.79) had significantly higher reading accuracy standard scores than the SLI-only subgroup (M = 82.73, SD = 12.52), β = , CI = to -1.82, p <.01. However, there was no difference between the two subgroups in terms of reading comprehension; β = -4.08, CI = to 1.33, p =.14; M = 79.11, SD = for the SLI+ASD subgroup and M = 77.62, SD = for the SLI-only subgroup. Interestingly, the discrepancy in the SLI+ASD subgroup was significantly larger than in the SLI-only subgroup, β = -5.75, CI = to -1.58, p <.01; M = 10.38, SD = 9.96 for the SLI+ASD subgroup and M = 4.59, SD = for

25 25 Reading Development in Children with SLI the SLI-only subgroup. These results provide evidence for differences in patterns of reading skills in individuals with SLI+ASD versus those with SLI-only. The Relationships between Language Related Abilities and Reading Skills in Subgroups of Individuals with SLI Regression analyses were used to investigate the relationship between language ability and reading skills using the age 14 data. In the following analyses, the relationship between reading accuracy and phonological memory was investigated. For reading comprehension, the relationship with receptive and expressive language ability was analysed. Reading Accuracy Standard scores for the Nonword Memory Test (NMT) were used in the following analyses. There was a marginal difference between the two subgroups, with the SLI+ASD subgroup displaying better phonological memory than the SLI-only subgroup, t(80) = 1.99, p =.05, d =.47 (see Table 5). Interestingly, the SLI+ASD subgroup was more comparable to what is expected from the typically developing population while the SLI-only subgroup was approximately 1SD below expectation. Correlations between phonological memory and reading accuracy were highly significant for both subgroups (r =.72 and.63, ps <.001, for SLI+ASD and SLI-only subgroups respectively). Regressions were then conducted controlling for PIQ at age 7 and gender. In the SLI+ASD subgroup phonological memory was significantly predictive of reading accuracy ability, β =.57, CI =.28 to.87, p =.001, adjusted R 2 =.48. Phonological memory also had a significant influence on reading accuracy in the SLI-only subgroup, β =.49, CI =.33 to.64, p <.001, adjusted R 2 =.43. -Table 5 about here- Reading Comprehension

26 26 Reading Development in Children with SLI The relationship between reading comprehension and receptive and expressive language was investigated next. There was no difference between the two subgroups in either receptive or expressive language, β = -1.99, CI = to 7.27, p =.67 and β = -4.62, CI = to 1.21, p =.12, respectively. See Table 5 for the descriptive statistics on receptive and expressive language for the two subgroups. The correlation between receptive language and reading comprehension was strong for both subgroups (r =.81 and.68, ps <.001, for SLI+ASD and SLI-only, respectively) as was the association between expressive language and reading comprehension (r =.83 and.67, ps <.001, respectively). Stepwise regressions were conducted with receptive and expressive language entered separately and then combined in the final analysis, with PIQ at age 7 entered as covariate. Models for reading comprehension that included receptive language or expressive language as single predictors explained 64% and 74% of the variance respectively in the SLI+ASD subgroup. When both receptive and expressive language were entered, a total of 75% of the variance in reading comprehension was explained. Expressive language was the strongest significant predictor of reading comprehension. - Table 6 about here - The pattern of findings for the SLI-only subgroup was similar. Expressive language was also the strongest predictor but receptive language also remained significant (p =.01) in the final model, which explained 58% of the variance in reading comprehension. Table 6 presents the regression results. Discussion The main findings of this longitudinal investigation provide evidence for the deficit model of reading development in individuals with a history of SLI. Individuals with SLI have lower reading accuracy and reading comprehension skills than

27 27 Reading Development in Children with SLI typically developing peers and they remain at the same lower level of relative ability from age 7 to 16 years. They do not catch up but nor do they fall further behind their age peers, as the developmental lag and slower growth models predict. The shape of the growth trajectories in reading skills is consistently parallel to what would be expected in their age peers, but at a lower level. That is, individuals with SLI exhibit a nonlinear trajectory of reading development with more rapid growth in childhood followed by a slowing down, i.e. plateau, in skills during adolescence (see Catts et al., 2008; Francis et al., 1996 for growth curves from typically developing populations). However, it must be remembered that the individuals within our study were all attending language units at 7 years of age. A more positive picture of improvement in reading skills across development may be observed in children with less severe early language difficulties. This study replicates Catts et al. (2008) who also found similarities between individuals with SLI and their typically developing peers in the nonlinear patterns of growth of reading skills from 7-8 years to years of age within the context of consistently parallel lower levels of skills for individuals with SLI. The current study reproduces these findings with a separate group of individuals with a history of SLI and, much like Catts et al., also provides evidence that these findings are robust to variations in performance IQ. This replication is significant, as the two samples differed in important aspects. Firstly, the current sample is a UK sample, whereas Catts et al. studied a US sample. Secondly, Catts et al. used an epidemiological sample with SLI status ascertained at around 5 to 6 years of age. The current sample was recruited at 7 years of age from language units across England and is thus a clinical, referred sample based on the identification of primary language difficulties and the requirement of language support during infancy and early school years.