Concurrent validity of the Bayley Scales of Infant Development II Motor Scale and the Peabody Developmental Motor Scales-2 in children with developmental delays.

Purpose: The purpose of this study was to explore concurrent validity of the age equivalent and standard scores of the Bayley Scales of Infant Development II (BSID II) Motor Scale and the Peabody Developmental Motor Scales-2 (PDMS-2), including correlations and clinical agreement between the scores of the two tests.

Methods: One hundred ten children aged three to 41 months who were referred to an early childhood evaluation program because of concerns about their development were administered both the BSID II Motor Scale and the PDMS-2 as part of their developmental evaluations.

Results: The correlation coefficients were high to very high for age-equivalent scores, and the Locomotion Subscale had the closest agreement with the BSID II Motor Scale age equivalent. The correlation coefficients were moderate to high for standard scores, and there was only slight agreement between the tests for standard score categories. More than 75% of the 70 children in this study whose scores on the BSID II supported eligibility for services based on scores at least two SD below the mean of the test would not have qualified for services if the PDMS-2 standard scores alone were used to assess their eligibility. Approximately half the children who showed appropriate total motor performance on the PDMS-2 were classified as delayed on the BSID II Motor Scale.

Conclusions: The study supports concurrent validity of the tests only for certain subscale age-equivalent scores, particularly the BSID II Motor Scale with the PDMS-2 Locomotion Subscale. The current findings suggest that the standard scores show poor agreement and have low concurrent validity. There are marked differences in the standard scores of the two tests that may affect a child's eligibility for services in some states, and therapists should be cautious when making clinical decisions based solely on standard scores of one test.