ECONOMISTS these days use their mathematical-statistical techniques to explore all sorts of social issues, as well as economic topics. For instance, Anne Case of Princeton and Lawrence Katz of Harvard have just examined the influence of role models on inner-city youths.Their findings should be no surprise. They confirm our general assumption that the behavior of parents and other close adults affects children. In a National Bureau of Economic Research paper, the two economists note that youths who had family members in jail when they were growing up are more than twice as likely to have committed crimes as those without family members in jail. Youngsters whose family members have drug or alcohol problems are almost twice as likely to use drugs themselves as those whose family members do not have such problems. Further, the best predictor of whether a youth will have a child out of wedlock is whether his or her parents were married. Also no surprise is the finding of Professors Case and Katz that young people living in a crime-ridden neighborhood - in this survey a low-income, inner-city Boston neighborhood - are more likely to engage in crime than those living in a neighborhood where fewer youths commit crime. All this sounds like the Old Testament saying: "The fathers have eaten sour grapes, and the children's teeth are set on edge." However, the two economists from Princeton and Harvard universities offer some hope: A few good influences, such as Sunday school, church, athletic programs, or other quality community programs can have a substantial positive impact on young people. Their findings may also serve as a warning to parents: If you want your children to behave, you had better behave yourself!