FREE hit counter and Internet traffic statistics from

Thursday, February 08, 2007

Losing Weight and Getting Younger

Wouldn't that be great?

This week my column on Baseball Prospectus focuses on the trend in decrease in player weight for players who debuted in the second decade of the twentieth century. After exploring a few theories as to why this occurred I zero in on the upsurge in the number of players used during that period which resulted in younger and therefore smaller players entering the game. The following graph shows the trend.

The remainder of the article discusses some of the reasons why this upsurge occurred and I draw an analogy between the experimentation in baseball during this period and the Burgess Shale fossils.


Guy said...

Dan: Very interesting analysis, as usual. One thing puzzled me: if players' recorded weight is done early in their career, that would mean older players' recorded weight -- as opposed to actual -- shouldn't be any higher than younger players'. So why then does the influx of young players reduce the mean weight?

Two related thoughts: perhaps the influx of new players brought players who were lighter because A) of the positions they played, and/or B) they were less talented, and so on average a little smaller (and less strong). For example, were a lot of the new players middle infielders? Or did pitchers weigh any more/less than hitters, and did the ratio of hitters: pitchers change? My own guess would be that "B" is the major factor.

Dan Agonistes said...

My thinking was that:

a) if the age of debut trended lower
b) if the weight was recorded early in their career
c) then the average weight of players at debut would be lower relative to other years since the weight of other players in the league who previously debuted would have been recorded at higher ages when they were heavier

In looking at the data more closely, weight flat lines from 1961-1965 and then has a spike in 1966 and then back to the line in 1967. It then trends a bit lower from 1971-1974 before moving back up again.

Still, I think you're correct about the talent (B) and its correlation with size and that may be the more relevant factor. As you mentioned in your email to me, "that interpretation is supported by the fact that weight decreased from 1943-46 despite average age skyrocketing. WWII meant an influx of inferior players, and that meant they were smaller (desite being older)."

That seems fairly convincing to me. Thanks