Our empirical findings are robust to controlling for individual fixed-effects, expe- rience, year effects, team, home ballpark characteristics, and managerial quality. The inclusion of individual fixed-effects means that the results cannot be explained by assorta- tive matching between complementary or substitutable players at the team level, since the analysis is exploiting variation over time within a given player’s performance. In addition, the results are robust to using a first-differences specification, as well as restricting the sample to only those workers who change teams (changing all of their co-workers), or using a sample of only those workers who remain with the same team, manager, and home ball- park in.
