For this analysis, we excluded children with congenital diseases (eg, blindness, cleft lip and palate, spina
bifida; n = 50), twins (n = 1650), or with developmental delay (Bayley Scales of Infant Development Mental [n = 450] or Motor score [n = 400] < 1.5 SDs below the
sample mean), as these children might have self - regulation problems that are significantly different from the general population.
For example, if one were interested in whether the association between a parenting variable (e.g., father psychological control; Holmbeck, Shapera, & Hommeyer, in press) and an outcome (e.g., school grades) is moderated by group status (e.g., spina
bifida vs. an able - bodied comparison
sample), one would test the interaction of psychological control and group as a predictor of school grades after controlling for the parenting and group main effects.