To investigate sampling bias, we compared demographic measures from participating and eligible non-participating families. Neither the percentage of parents remaining married, mean family income, father's years of education, nor mother's occupational status differed significantly between participating and non-participating families. Years of education, however, were significantly higher among participating mothers (M=14.3, SD=1.9) than among nonparticipating mothers (M=13.8, SD=2.0) (p<.01), and occupational status indicators (codes ranged from 1 to 7, with 7 reflecting the highest status) were higher among participating fathers (M=4.7, SD=1.7) when compared with nonparticipating fathers (M=4.2, SD=1.8) (p<.01). While this indicates some degree of positive selection, the effect appears to be slight. Standardized effect-size estimates equal .26 and .29 for mother's education and father's occupational status, respectively. Thus, the sample is generally representative of the population from which it was drawn.
