COMPARISON OF THE MULLEN SCALES OF EARLY LEARNING AND THE BAYLEY COGNITIVE SCALE, 3RD EDITION, IN ASSESSING NONVERBAL IQ IN TODDLERS WITH AUTISM SPECTRUM DISORDERS

Background: The Bayley and Mullen scales are commonly used measures of cognitive skills in toddlers, with the Mullen used frequently in research involving children with autism spectrum disorders (ASD).  The Mullen and Bayley-III are the only standardized measures of nonverbal cognitive functioning for children under age 2.  Convergent validity was examined for the Mullen and original Bayley Scales of Infant Development, with small to moderate correlations (Mullen, 1995).  Neither measure has been investigated with regard to convergent validity in young children with ASD. Validity of nonverbal cognitive scores is particularly relevant for young toddlers with ASD, who are likely preverbal, as they provide information on overall development.

Objectives: Examine the convergent validity of Mullen nonverbal scales with Bayley-III cognitive scales in a sample of toddlers age 2 years with ASD.

Methods: Participants were over 50 children in the Toddler Talk Project, a longitudinal study on language development of children with ASD.  Children are seen yearly, starting at age 2 until age 5.  ASD diagnoses were determined using full diagnostic evaluations that included the ADI-R and ADOS.  The Mullen and Bayley-III were given at the same appointment at the 2-year-old visit.

Results: Preliminary results indicated strong correlations between the measures for nonverbal mental age; standard scores were not correlated.  A significant number of children had differences in standard scores greater than 1 SD, putting them into a different qualitative score range on each measure.  In almost all cases, standard scores on the Mullen were lower.

Conclusions:   Nonverbal IQ has been identified as an important predictor of later functioning (Lord et al., 2006). It has important implications for research, as it often is used as a primary variable. Caution should be taken in interpreting nonverbal standard scores for toddlers with ASD using the Mullen or Bayley-III.  Age equivalent scores showed good agreement.