Increasing mental development index in Australian children: A comparative study of two versions of the Bayley Mental Scale

Abstract

Original and revised editions of the Bayley Scales of Infant Development were administered to 97 healthy infants aged 18 to 27 months. Concurrent scores on the Mental Development Index (MDI) were consistent with an average increase of approximately 18 points over the past 25 years. MDI gains varied from 4 to 35 points and were apparent for both genders and for infants from different cultural backgrounds, but they were marginally higher for females than for males, and significantly higher for Australian infants in comparison to infants from non-English-speaking families. No significant effect was found for age. These gains for Australian infants were higher than those reported for an American infant population. Although the gains observed in all levels of intelligence ranged from -1 to 2.2 standard deviations, there was significantly more improvement for higher scoring infants than for infants in the normal range. This finding was, therefore, similar to IQ gains which have been reported for older children and adults. The results suggest that norms for the first version of the Bayley Scales of Infant Development, and probably for all other infant developmental scales that have not been updated, now have questionable research and clinical utility.