A clinically interpretable method for analyzing the bayley infant behavior record

To provide an empirical basis for considering certain infant behavior patterns during developmental testing to be abnormal or deviant, Bayley Infant Behavior Record (IBR) data were examined from two large nor mative U.S. samples, the Bayley Standardization Sample (BSS) and Louisville Twin Study (LTS). The two samples were consistently in agree ment in that their cumulative frequency distributions for 15 of the 16 general IBR rating scales manifested sharp discontinuities that were relatively invariant between the ages of 6 and 30 months. These observa tions guided a method providing ident behaviors that can be suspected to be abnormal because they are both poorly adaptive and infrequently observed in normal infants.