Objectives: The present study aimed to compare the performance of Iranian Azeri-speaking children based on Iran and the reference of the Bayley Scales of Infant and Toddler Development Third Edition (Bayley III) norms.
Materials & methods: The total sample included 248 infants and toddlers aged 16 days to 42 months and 15 days. The Iranian version of the Bayley III scale was used in this study. The scaled scores and composite scores in cognitive, language, and motor domains were compared based on Iran and reference Bayley III norms. Then, the proportions of children scoring < -1 standard deviation (SD) and < -2 SD were compared based on the two norms.
Results: The scaled scores of the study group were higher based on the reference norms in receptive communication, fine motor, and gross motor subtests. The scaled scores were variable in expressive communication and cognitive subtests. The differences were significant for receptive communication and fine motor subtests (P<0.05). Using the reference norms instead of Iran norms resulted in under-referral regarding receptive communication and fine motor subtests. More children scored below 1 and 2 SD using Iran norms in comparison to those reported for using the reference norms.
Conclusion: Iran norms differ significantly from the reference norms over two subscales. It is recommended to use population-specific norms to identify children with developmental delay and early intervention.
Keywords: Bayley III Norms; Bayley III Scales; Cognitive; Iranian Children.