age revisited

Commenter Tom, in response to Tuesday's post regarding average ages of pitchers who have hit Craig Biggio with a pitch, asked how the average age of those pitchers compared with the leaguewide averages for each season. So, I looked. Ideally, I would have liked to use complete game logs for all players to calculated their exact age on each date on which they pitched and use all of those for a weighted average to represent each season, since that is how the average ages of the pitchers who hit Biggio with pitches was calculated, but for the entire population, that method is impracticle. Instead, each pitchers age has been calculated as of July 1 of each season in which they pitched. That should be close enough for an investigation of stats related to people getting hit by pitches.
As you may recall, the average age of pitchers who hit Craig Biggio with a pitch was 28.5 at the end of the 2005 season. For players who pitched between 1989 (the first year Biggio was plunked) and 2005, the average age of pitchers in the league was 28.6 - so overall, it has been younger than average pitchers who have been plunking Biggio. Over that same span, the average age of pitchers who hit at least one batter was 28.78 years. That may look as though older pitchers are more likely to hit a batter, but it's more a matter of older pitchers being more likely to have enough time to hit a batter. The average age of pitchers who threw more than 10 innings in a season, over that same span, is 28.80 years, so it looks as if the leaguewide average is lowered by a number of young pitchers who have very brief stints in the majors during a given season.
While the overall average age of pitchers who have plunked Biggio has been lower than the league average, Biggio plunkers have been younger than average in only 8 of 17 seasons. For the past two season, those pitchers who hit Biggio have been older than average by 0.26 years in 2005, and 0.08 years in 2004. The largest difference was in 2000 when pitchers who hit Biggio with a pitch were 3.24 years older than the league average. Not coincidentally, that was the year Biggio plunkers had the oldest average age. The year they had the youngest average age also corresponds with the largest difference in that direction - in 1997 when those who plunked Biggio were 1.69 years younger than average. The average age of the relatively small sample of pitchers who hit Biggio has shown much more variance compared to the whole pitching population, which has remained fairly stable from year to year. But, there does appear to be an upward trend in the average age of pitchers, and there is probably an overall increase in average age of major league players.
(Last year, there were 19 players in the league over the age of 40 by April 1st - the most ever. By percentage of the total league population it was the highest since the late 1940s when there was an understandable lack of baseball aged men around. I think there were 17 who have played this season who were over 40 as of April 1st.)

Here is the year by year comparison of average age of pitchers who hit Craig Biggio with a pitch, with the leaguewide average for pitchers, and the average age for pitchers who hit at least one batter:

	Pitchers who hit Biggio	All Pitchers		Pitchers with at least 1 HB
Year	Avg Age	Avg Age	Diff	Avg Age	Diff
2005	29.32	29.06	0.26	29.29	0.03
2004	29.02	28.94	0.08	28.98	0.04
2003	28.04	28.84	-0.80	28.84	-0.80
2002	27.89	28.73	-0.84	28.91	-1.02
2001	27.31	28.77	-1.46	28.80	-1.49
2000	31.99	28.75	3.24	28.93	3.06
1999	31.15	28.52	2.63	28.95	2.20
1998	28.50	28.62	-0.12	28.95	-0.45
1997	26.76	28.45	-1.69	28.45	-1.69
1996	27.99	28.30	-0.31	28.41	-0.42
1995	28.67	28.24	0.43	28.43	0.24
1994	29.09	28.63	0.46	28.79	0.30
1993	30.06	28.44	1.62	28.63	1.43
1992	27.11	28.58	-1.47	28.84	-1.73
1991	29.67	28.27	1.40	28.53	1.14
1990	27.32	28.34	-1.02	28.38	-1.06
1989	30.21	28.52	1.69	28.85	1.36