We appreciate the recent article by the Victoria Infant Collaborative Group1 and the editorial by Dr Msall2 voicing concern about underestimation of developmental delay by the Bayley Scales of Infant and Toddler Development–III (Bayley-III).
The Bayley Manual3 provides information about the Flynn effect, as mentioned in the Victorian Study.1(p355) The Bayley-III manual sample of 102 children gives the average Mental Developmental Index (MDI) of the Bayley Scales of Infant Development–II (BSID-II) to be 93.9 and the Bayley-III Cognitive and Language Composite Scores (CSs) to be 102 and 99.7, respectively.3 The latter CS differences from the MDI are 8.1 and 5.8 points, with corresponding correlations of 0.60 and 0.71.3(p77) Overall, Bayley-III CSs are 7 points higher than those of the BSID-II, and thus show a reverse Flynn effect.
Robertson CMT, Hendson L, Biggs WSG, Acton BV. Application of the Flynn Effect for the Bayley III Scales. Arch Pediatr Adolesc Med. 2010;164(11):1072-1073. doi:10.1001/archpediatrics.2010.199