Author: Christopher Lee

  • Birth Month Effect On Baseball Performance, Part II

    In our first post, we showed the percentage of players in Major League Baseball based on birth month.  As I showed, there is a much higher percentage of players born in August, largely due to the Little League Baseball cutoff date of July 31.

    In order for players to reach the majors, they had to have been performing at a higher level through various levels of baseball.  But once they reach the major league level, is there any correlation between birth month and performance? Let’s take a look.


    Note: Batting Performance Chart Returning Soon

    Interestingly, the statistics show that, if anything, players born in JULY outperform those born in August.  While 2 HR and 5RBI isn’t huge, it still interesting to see that players born in July outperform those born in August.


    Note: Pitching Performance Chart Returning Soon

    There is very little difference in pitching statistics relative to birth month.  Players born in August pitched more innings, and had a slightly lower ERA, but no extreme differences between people born in July and August.


    Wile there was a huge difference in the percentage of players born in July (6.4%) compared to August (12.2%), the difference in performance was fairly small.  How could this be?

    The theory is that by the time a player reaches the Major League, they are an expert, and thus in aggregate the statistics are very similar.  Any other thoughts?  There are more players born in August, yet their performance isn’t any better.  What other explanations can you think of?

  • Birth Month Effect On Baseball Players, Part I

    The birth month phenomena is an interesting occurrence that is applicable throughout society.  While Outliers by Malcolm Gladwell implied the same was true for baseball, I wanted to take a closer look.  Looking at the birth month of every MLB player that has appeared in a game since 1965, the graph suggests that you’re most likely to become a MLB player if you are born in August.

    Among US born players, 12.2% of MLB players have birthdays in August, while only 6.4% have birthdays in July. A discrepancy that big can’t just happen by accident can it?  Not likely.  The reasoning is that the Little League Baseball cutoff date for 55 years (up until 2006) was July 31.

    So what does that mean?  A player, for example, born on August 1, 1996 would be playing in the same division as a kid born on July 31, 1997.  Given the cutoff date, the kid with a birthday on August 1 is a year older than the kid with a birthday on July 31 yet they are playing in the same division.  Thus, the player with the birthday in August likely has an advantage in size, strength and maturity.  Players with birthdays in August may be more likely to get picked for All Stars, get advanced training and practice, and selected for more competitive leagues which ultimately helps make them a more successful player.

    Interestingly, in 2006 Little League changed the cutoff date to April 31, so if you want your kid to have a leg up on the competition, a May birthday will be most beneficial.

    So if players born in August are more likely to become MLB players, do they perform better at the Major League level?  Stay tuned for Part II in a few days.

    Data Source: Sean Lahmans’