The Associated Professional Sleep Societies is busy holding its 25th Anniversary Meeting in Minneapolis, and the meeting has produced 340 pages of abstracts and a flurry of press releases, generally focused on various aspects of nodding off. One of the exceptions tackled the related issue of circadian rhythms, the daily cycles of sleep and wakefulness, using a somewhat unexpected measure of performance: professional baseball. When it comes to batting, it looks like there may actually be morning people and night owls.

On its own, this isn't a bit of a shock. Chronotypes exist in many animals, and have been linked to a variety of performance tendencies, with different people peaking at different times of the day. There's even a survey, the Morningness Eveningness Questionnaire, that helps assign people to one of the two categories in the survey's title. The shock might be how large the impact of chronotype appears to be at the professional level.

The researchers took data from 16 pro baseball players, nine of them evening types. They then took two years of game data, dividing it up into early, middle, and late games (The middle category was between 14:00 and 19:59, with the other two on either side of that). Differences with the player's home time zone due to travel were taken into account. Altogether, over 7,000 innings of data were processed for these 16 players.

The results? Morning players batted .252 for all of the later games—for the earliest category, however, they hit .267. The night owls hit around .260 until things got late, after which they caught fire, hitting .306. It's a preliminary result, but it strongly suggests that baseball players hit according to their chronotype. The authors, one of whom works for the San Francisco Giants, plan on expanding the number of players they track and getting a finer-grained view of the time of a given at bat in order to see whether this effect really holds up. It might be that, for some players, it will make sense to ride the bench if a game has a late start.