[position in research by date]
[position in research by subject]
"Estimated Age Effects in Baseball,"
2008, Journal of Quantitative Analysis in Sports, Vol. 4: Iss. 1,
Age effects in baseball are estimated in this paper
using a nonlinear fixed-effects
regression. The sample consists of all players who have played 10 or
more ``full-time'' years in the major leagues between 1921 and 2004.
Quadratic improvement is assumed up to a peak-performance age, which
is estimated, and then quadratic decline after that, where the two
quadratics need not be the same. Each player has his own constant term.
The results show that aging effects are larger for pitchers than for
batters and larger for baseball than for track and field, running, and
swimming events and for chess. There is some evidence that decline rates
in baseball have decreased slightly in the more recent period, but they
are still generally larger than those for the other events.
There are 18 batters out of the sample of 441 whose performances
in the second half of their careers noticeably
exceed what the model predicts
they should have been. All but 3 of these players played from
The estimates from the fixed-effects
regressions can also be used to rank players. This ranking differs from
the ranking using lifetime averages because it adjusts for the different
ages at which players played. It is in effect an age-adjusted ranking.