Reassessing the association between facial structure and baseball performance: a comment on Tsujimura & Banissy (2013).

Are the associations between the facial width-to-height ratio (fWHR) and Japa-nese male baseball player performance documented by Tsujimura & Banissy [1] robust to controlling for body mass index (BMI)? Two factors motivate this question. First, research suggests that BMI is positively associated with both home run hitting [2,3] and fWHR [4,5]. Second, recent research has suggested that body size, not facial fWHR, predicts outcomes among male professional hockey players [6,7]. Regression analysis is used to reassess the positive associations between fWHR and home runs, runs-batted-in and slugging percentage [1] while controlling for BMI. Poisson estimation is used for the count-based performance metrics of home runs and runs-batted-in, while ordinary least-squares estimation is used for the continuous performance variable slugging percentage [8]. Player performance, fWHR and number of at-bats are from Tsujimura & Banissy [1]. BMI is calculated as (weight/height 2) Â 703. Player weight (in pounds) and height (in inches) are obtained from www.baseball-reference. com, which is also used to collect data on player age, whether a player bats right-handed and the player's team. Controlling for handedness is important given right-handed individuals exhibit higher levels of circulating testosterone [9]. Including team indicator variables alleviate stadium effects and home field advantage [10] that can impact player performance. For example, if an outfield fence of a given stadium is relatively closer to home plate, the team calling that stadium home will play more games there than other teams, thereby increasing home run hitting potential. The data contain 206 player-year observations across the two seasons analysed, representing 125 unique players (data available as electronic supplementary material). The Pearson correlation between fWHR and BMI for this set of unique players is positive and statistically significant (r(125) ¼ 0.218, p ¼ 0.015), suggesting the potential for confounding BMI effects. Columns (A) and (D) in panel I of table 1 show a positive and statistically significant association between home runs hit and fWHR in both the 2011 (coefficient ¼ 3.384, p , 0.01) and 2012 (coefficient ¼ 2.445, p , 0.01) seasons, after controlling for lognormalized at-bats and player age [1]. Column (B) and (E) introduce BMI as an additional control. The coefficient on BMI is positive and statistically significant in both the 2011 (coefficient ¼ 0.176, p , 0.01) and 2012 (coefficient ¼ 0.154, p ¼ 0.01) seasons, and fWHR is no longer a statistically significant home run predictor. In columns (C) and (F), batting …