CrossSectional and Longitudinal Analyses of the Receptive

1
Cross-Sectional and Longitudinal Analyses of the
Receptive Vocabulary Ability of Individuals with
Williams Syndrome Rebecca L. Johnson and Carolyn
B. Mervis Department of Psychological and Brain
Sciences, University of Louisville

• RESULTS
• QUESTION 1
• To address Question 1, we first calculated
  descriptive statistics for the standard scores of
  the cross-sectional sample.
• Mean 78.98
• SD 13.36
• Range 40 to 117
• We then made a histogram (Figure 1) to examine
  the distribution of PPVT-III standard scores.
• As indicated in Figure 1, PPVT-III standard
  scores are normally distributed for individuals
  with Williams syndrome.
• The mean standard score of the sample (78.98) is
  1.40 SD below the mean standard score of the
  general population.

• QUESTION 3
• To address Question 3, we plotted the PPVT-III
  standard scores of the cross-sectional
  participants as a function of their chronological
  age (Figure 3).
• r .01
• df 122
• This very low correlation indicates that, on
  average, receptive vocabulary ability of
  individuals with Williams syndrome relative to
  CA-matched individuals in the general population
  does not vary as a function of CA.
• That is, on average, individuals with Williams
  syndrome hold a consistent position relative to
  the general population across the entire range of
  CA tested (4 - 49 years).

• INTRODUCTION
• Williams syndrome is a genetic disorder caused
  by a microdeletion of the long arm of chromosome
  7 (7q11.23). Affecting 1/20,000 live births,
  Williams syndrome is characterized by dysmorphic
  facial features, mild to moderate mental
  retardation (75) or learning disabilities
  (25), a unique gregarious personality, and a
  distinctive cognitive profile. Individuals with
  William syndrome evidence relative strength in
  the areas of auditory rote memory and language
  and have most difficulty with tasks that require
  visual-spatial construction skills.
• The purpose of this study was to explore the
  receptive vocabulary abilities of individuals
  with Williams syndrome across a wide age range.
• RESEARCH QUESTIONS
• QUESTION 1
• What are the receptive vocabulary capabilities
  of individuals with Williams syndrome relative to
  those of the general population?
• QUESTION 2
• Do the receptive vocabularies of individuals
  with Williams syndrome continue to increase
  across the lifespan?
• QUESTION 3
• Is the receptive vocabulary level of individuals
  with Williams syndrome relative to their
  CA-matched normally developing peers maintained
  across the lifespan?
• METHOD
• PARTICIPANTS

• QUESTION 3 (continued)
• As indicated in Table 1, standard scores, on
  average, showed no change when individuals were
  tested over time.
• The standard deviation of the Williams syndrome
  group is similar to that of the general
  population.
• A matched pairs t-test confirmed that receptive
  vocabulary ability relative to the general
  population is consistent over the time interval
  included in this study.
• t (20) -.02
• p .98
• DISCUSSION
• The receptive vocabulary capabilities of
  individuals with Williams syndrome are
  significantly below that expected for CA-matched
  peers in the general population.
• Average performance is in the borderline normal
  range.
• Nevertheless, the shape of the distribution of
  standard scores is similar to that of the general
  population.
• Standard scores are normally distributed.
• The standard deviation is similar to that of the
  general population, indicating a similar amount
  of variability but a lower mean level of
  performance.