Factor Structure of the Aberrant Behavior Checklist in Individuals with Fragile X Syndrome: Clarifications and Future...

The Aberrant Behavior Checklist (ABC) is a standardized rating scale used for assessing problematic behavior of individuals with developmental disabilities. It has five subscales: Irritability, Social Withdrawal, Stereotypic Behavior, Hyperactivity, and Inappropriate Speech. A previous study in individuals with fragile X syndrome (FXS) reported six factors, with the Social Withdrawal factor bifurcating into Socially Unresponsive and Social Avoidance factors, suggesting a different factor structure in people with FXS. We assessed the ABC's factor structure (with both exploratory and confirmatory analyses) in 797 people with FXS and we compared these findings with exploratory factors derived from an independent sample of 357 individuals with FXS. In an ancillary analysis, we compared the overlap of the traditional ABC's Social Withdrawal scores with the Social Avoidance scores from the FXS-derived newer scale to determine whether overlap between these was very high and essentially redundant. Finally, we computed norms using both the traditional and the FXS-specific algorithms. In confirmatory factor analyses, the FXS-specific algorithm produced the most consistent factor structure for the sample of 797 participants, but model fit was only marginally better than that derived by the original ABC scoring algorithm. Comparisons of factor structures from separate exploratory analyses revealed no consistent advantage of the FXS algorithm over the traditional algorithm. While a Social Avoidance subscale did emerge in some analyses, in other analyses, this was accompanied by loss of coherence on other domains of interest, such as the Socially Unresponsive/Social Withdrawal subscale. We question whether the newer FXS scoring algorithm contributes data that are consistently helpful in evaluating behavior of people with FXS. In general, we recommend continued use of the original ABC algorithm for scoring behavior of clients with FXS. However, we acknowledge that there may be circumscribed times when the new algorithm may be appropriate for scoring, namely when anxiety and/or social avoidance constructs are the central and unequivocal domains of interest.