Hitting Is Contagious in Baseball: Evidence from Long Hitting Streaks

Abstract

Data analysis is used to test the hypothesis that "hitting is contagious". A statistical model is described to study the effect of a hot hitter upon his teammates' batting during a consecutive game hitting streak. Box score data for entire seasons comprising 28 streaks of length L≥30 games, including a total 4,496 observations were compiled. Treatment and control sample groups (n=151) were constructed from core lineups of players on the streaking batter's team. The percentile method bootstrap was used to calculate 95 confidence intervals for statistics representing differences in the mean distributions of two batting statistics between groups. Batters in the treatment group (hot streak active) showed statistically significant improvements in hitting performance, as compared against the control. Mean BA for the treatment group was found to be 1.6 to 20 percentage points higher during hot streaks (mean difference increased 11.1 points), while the batting heat index Q introduced here was observed to increase by 32 points. For each performance statistic, the null hypothesis was rejected at the α=0.05 significance level. We conclude that the evidence suggests the potential existence of a "statistical contagion effect". Psychological mechanisms essential to the empirical results are suggested, as several studies from the scientific literature lend credence to contagious phenomena in sports. Causal inference from these results is difficult, but we suggest and discuss several latent variables that may contribute to the observed results, and offer possible directions for future research. © 2012 Bock et al.