Longitudinal Assessment of
Receptive Vocabulary in Children
and Adolescents with Williams
Syndrome: A Multilevel Modeling
Analysis
-
1
University of Wisconsin-Milwaukee, United States
Statement of Purpose: It is widely accepted that concrete vocabulary and verbal short term memory are relative strengths of children and adolescents with Williams syndrome (WS). Mervis and Becerra (2007) reported an average standard score (SS) of 79.9 (sd = 13.6) on the Peabody Picture Vocabulary Test- III (PPVT-III; a measure of receptive concrete vocabulary) for 238 children (ages 4 – 17 years). PPVT-III SS were uncorrelated (r = - .12) with chronological age (CA), suggesting no developmental change. The purpose of the present study was to examine the relation between CA and receptive vocabulary longitudinally and to document individual differences in the stability of receptive vocabulary in children and adolescents with WS.
Methods: Participants were 63 individuals with WS who had completed the PPVT-III at least 3 times (median = 4 times, range = 3 – 10) and who were 4 – 19 years old at the time of first assessment. Participants also completed the Differential Ability Scales (DAS) Recall of Digits subtest, measuring verbal short-term memory. Each participant’s mean Recall of Digits T score was used as a predictor of individual differences in receptive vocabulary. We used multilevel modeling techniques (Raudenbush, Bryk, & Congdon, 2002; Singer & Willet, 2003) to analyze individual change in PPVT-III SS over time periods averaging 5 years (range 2 – 10 years). Since the 63 participants varied in age at the time of their first assessment, we were able to model the developmental trajectories over an age range of 4 to 20 years. The advantage of the multilevel modeling approach is that both within-person and between-person data are analyzed to estimate the average developmental trajectory and the extent to which individual change over time differs from the average trajectory. Multilevel models were fit using HLM 6.0 and full maximumlikelihood estimation. Goodness-of-fit was assessed for each model tested using Chi- Square Deviance tests.
Results: Inspection of individual data suggested that some young children show sharp declines while others show little change or actually improve. However there was less change during adolescence. Consequently the data were modeled by relating PPVT-III SS to log CA (centered at age 10 years). The average trajectory is shown in the figure. The average intercept, which represents the estimate of average performance at age 10 years, was 83.9 and the average slope was -5.9 per log year, resulting in an average decline of 9 points between the ages of 4 and 20 years. There was significant individual variability in both intercepts (SD = 8.8) and slopes (SD = 10.0). Digit Recall T score was a significant predictor of individual variability in intercepts (i.e., overall level) but was not a significant predictor of variability in slopes (i.e., change over time). For each 1 point increase in Recall of Digits T score, PPVT-III intercepts increased roughly 1 point.
Discussion: On average, PPVT-III SS for individuals with WS decreased significantly from age 4 – 20 years, showing the most decline between ages 4 and 10. These results underscore the importance of longitudinal data for estimating developmental change and documenting individual differences in language and cognitive abilities.
Conference:
12th International Professional Conference on Williams Syndrome, Garden Grove,CA, United States, 13 Jul - 14 Jul, 2008.
Presentation Type:
Poster Presentation
Topic:
Multidisciplinary Poster Session
Citation:
Mervis
CB,
Kistler
DJ,
Peregrine
E and
John
AE
(2009). Longitudinal Assessment of
Receptive Vocabulary in Children
and Adolescents with Williams
Syndrome: A Multilevel Modeling
Analysis.
Conference Abstract:
12th International Professional Conference on Williams Syndrome.
doi: 10.3389/conf.neuro.09.2009.07.053
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Received:
04 May 2009;
Published Online:
04 May 2009.
*
Correspondence:
C. B Mervis, University of Wisconsin-Milwaukee, Wisconsin, United States, cbmervis@louisville.edu