At age 48, we interviewed 61% (523, 255 females, 268 males) of the original sample of 856. Of the noninterviewed participants, 37 were confirmed dead, 112 had disappeared and could not be found despite intense efforts, 40 could not be interviewed because of distance and scheduling difficulties, and 144 refused. The number who refused to be interviewed (despite substantial financial incentives) was higher than expected, but the completed re-interview rate of 61% over 40 years still provides us with a sizable sample for analysis. However, we must ask whether the attrition introduced bias into the sample. A comparison of means on age 8 scores revealed that compared with participants who were re-interviewed at age 48, participants who were not re-interviewed had higher levels of aggression, t(854)=4.06, P<.001 (Mdifference=0.13, SEdifference=0.03), lower levels of popularity, t(854)=4.19, P<.001 (Mdifference=4.45, SEdifference=1.06), lower anxiety about behaving aggressively, t(854)=3.86, P<.001 (Mdifference=3.40, SEdifference=0.88), and lower IQ at age 8, t(852)=5.69, P<.001 (Mdifference=5.70, SEdifference=1.00). These effect sizes range from r=.14 to .19. However, we note that the plots of the distributions for these four age 8 variables revealed
