It was originally intended that a three-way interaction between sex, age, and behavior of nominated best friends at T1 be included in the model. However, a power analysis using a hypothetical effect size of .05 for a three-way interaction (estimated based on the effect size obtained for the significant two-way interaction) indicated that a sample size of N = 320 was required to adequately test the three-way interaction. This interaction was consequently dropped from the final analysis. Significant main and interaction effects of between-subject factors were probed using Gabriel's test of post hoc comparisons. This test was chosen because of its suitability in situations where sample sizes are unequal. All analyses were conducted using the Statistical Package for the Social Sciences (SPSS) v.18.