ALTRUISM AND THE FAMILY FIRM : SOME THEORY Columns E and F explore the impact of varying the sample definition. In Column E, the basic model is estimated on public schools only, while in Column F the 18 MSAs that have only a single district are excluded. The choice-peer group interaction coefficient is again negative in each of these specifications, significantly so (and with a substantially larger point estimate than in the basic specifications) in the latter case.