The Bayley Scales of Infant Development II: Where to start?

This study examines whether the Bayley Scales of Infant Development-Second Edition (Bayley II) Mental Scale scores vary on the basis of which item set is considered the starting point of an infant's assessment. The Bayley II was administered to 78 12-month-old infants by certified examiners beginnin g with the 12-month age item set. A second certified examiner then administ ered 10 additional items that completed the Ii-month and 13-month age item sets. Of the 78 infants tested, 73 (94%) met basal and ceiling criteria in all three item sets. Three separate Mental Developmental Index (MDI) scores were calculated using le-month norms for each subject, which were based on the raw scores generated from the 11-, 12-, and 13-month age item sets. Sc ores calculated on the Ii-month set were significantly lower than those on the 12-month set, which were in turn significantly lower than those on the 13-month set. When tested on the Ii-month instead of on the 12-month item s et, twice as many infants received lower than normal (<85) MDI scores, indi cating an impact on referability decisions. Minor adjustments in administra tion of the Bayley II, such as those based on assumptions regarding an infa nt's current level of functioning, significantly affect infant test scores and eligibility for follow-up services. Standardized use of this test shoul d minimize variability in test scores.