Tuesday, May 14, 2013

Aging and Performance

I've had the data for years to measure the impact that age has on baseball players, but was fooled for ages by a very basic conundrum, one I should have been smart enough to see through. I'll illustrate my dilemma with this stat line:
129 517 411 81 135 23 2 26 85 98 49 .328 .458 .584 1.042 179
Provided by Baseball-Reference.com: View Original Table
Generated 5/13/2013.

That's a solid season--led his league in batting, led the majors in OBP and OPS, played a significant number of games, excellent power. That was Ted Williams in 1958--at the age of 39.

What I used to do was simply group all players by age and look for an expected increase in whatever metric I was using (typically slugging, sometimes average) from around age 22-28, observe a plateau from 28-32 and then a slow and steady decline from 33 onward. The data doesn't show this--it often shows batting averages and slugging percentages staying roughly equal. It wasn't until I realized the obvious that I understood that I had to present the data in a different way. To provide an opening illustration, I'll use an example from football:
These are both relatively recent running backs, and this shows their production in the first four years of their career. As luck would have it, both started their careers at age 23 (and all ages used from hereon are those as stipulated by Baseball-Reference.com or Pro-Football-Reference.com), and it's pretty obvious they had success in the early part of their careers. In fact, these two players are the 1st and 3rd-most productive running backs in NFL history in terms of yardage in the first four years of their career. The next chart shows the rest of their careers:

Year 4 was effectively year LAST for the first running back, whereas the second one had three more productive seasons before succumbing to the usual declines that running backs meet when they reach the age of 30. In case it isn't obvious (or you didn't click the link above), the first running back is Terrell Davis and the second Eric Dickerson

My eureka moment was when I realized that if a player produced, they would still be in the game, and if they didn't, they weren't, which is why the numbers I was seeing for the older players still stayed as high as they did--if they hadn't, THEY WOULDN'T HAVE BEEN PLAYING. Once I realized that, I knew how to present the data, which is to show what percentage of players in the majors are at a given age range--the ranges I'll use are:
1. Under the age of 24--generally speaking, still developing and working their way into regular play
2. Ages 24-27--the beginning of the prime years
3. Ages 28-31--the prime years 
4. Ages 32-35--the separating of those who are productive from those whose skills are diminishing
5. Ages 36-39--players that are so special that they're still able to contribute
6. Ages 40+--the true Methuselahs

This will only cover HITTERS, since pitching is different and (I suspect) has different aging patterns, but I'll withhold judgment until I see the data. This first chart shows those ballplayers age 23 and under from 1901-2012, with explanations to follow:

There are two important considerations, and I'll use the under 20 category to explain. The blue line is the percent of players (again, position players only) that were under the age of 20, and that number has never been very high and has disappeared over the past 30 years or so. There were brief spikes in the 1910s, again in the 40s (primarily due to World War II) and another brief resurgence in the 50s, but teams recognize the value of getting their young players reps in the minors vs. pine time in the majors. The pink line is even more important, because that's the percent of plate appearances these young phenoms got, and even in the years with spikes, they didn't get many.

In the modern game, players are brought up to play, particularly as pitching staffs expand to 12-13 players--there's just no room on a roster to "season" these players anymore, which explains why the gap between percent of players and percent of plate appearances has diminished. The level has stabilized at around 10% of players that are under the age of 24. This next chart shows players aged 24-31:

Very busy slide but very basic message--these are players that are in the primes of their careers, but in two very different places on the continuum:
1. Players aged 24-27 are usually the value players, still playing on their first contract or having signed team-friendly deals early in their career (Evan Longoria, Anthony Rizzo just this past week, etc.) that gave them money and security but probably below what they could have received on the open market. Unless a team is the Yankees or Red Sox, these value players are the difference between success and failure. They're probably not quite at their peak career value, but getting very close.
2. Players aged 28-31 are absolutely in the prime of their careers--or are gone. By this age, teams know what they have, absent late bloomers like Jose Bautista, Ryan Ludwick and others who took their time in developing. Of course, these things happen--in particular with power hitters, they can develop late.

There is very little movement over time in this chart--they were about 63% of players in 1901, 67% in 2012, and there's nothing shocking about this. There appeared to be a trough in the 28-31 players in the 1910s, but that's more a function of numbers, in that there was another Major League in 1914-1915, the Federal League, which gave more playing opportunities, typically to players on the extremes of the spectrum--the very young or the very old. That trough effectively ended when the Federal League folded after the 1915 season. This next chart shows where change begins with players aged 32-35:

This is the age that separates the Hall of Famers from the also-rans, since a HOFer maintains productivity through this age span, and the others can't for any number of reasons--injuries, decline, etc. This is demonstrated by the lack of gap between the percent of players and percent of plate appearances--particularly in the modern era, if these players aren't regulars or key substitutes, they're too expensive to keep on a roster and will be replaced by younger and cheaper players. There is a rather precipitous increase beginning around 1973 which coincides with the introduction of the designated hitter, but there's just as steep of a decline that began very recently, falling from around 20% of players to 15%. How much of this is payroll-driven vs. player-breakdown reasons is for future historians to determine. 

This is the slide that will "puzzle" people in the future--players 36 and older:

In 2012, six players over the age of 40 were in the majors:
1 Henry Blanco 2012 40 ARI 21 67 64 6 12 3 0 1 7 3 18 .188 .224 .281 .505
2 Jason Giambi 2012 41 COL 60 113 89 7 20 4 0 1 8 20 24 .225 .372 .303 .675
3 Raul Ibanez 2012 40 NYY 130 425 384 50 92 19 3 19 62 35 67 .240 .308 .453 .761
4 Chipper Jones 2012 40 ATL 112 448 387 58 111 23 0 14 62 57 51 .287 .377 .455 .832
5 Jim Thome 2012 41 TOT 58 186 163 17 41 7 0 8 25 22 61 .252 .344 .442 .786
6 Omar Vizquel 2012 45 TOR 60 163 153 13 36 5 1 0 7 7 17 .235 .265 .281 .546
Provided by Baseball-Reference.com: View Play Index Tool Used
Generated 5/14/2013.

Jones retired and Thome and Vizquel are not on rosters. The steep decline from around 2000 illustrates that the ability to outfox Father Time seems to have disappeared. Giambi and Ibanez are getting semi-regular play and Blanco is trying to become the first player to be the backup catcher for every major league team (that's harsh--he's only played for ten teams). There was a spike in the 80s that included players like Darrell Evans, Rusty Staub, Pete Rose and Graig Nettles, and I'm sure one factor in the gradual increase in older players playing is the increased salaries that free agency ushered in. They're playing--but are they playing WELL?

It's too soon to tell, but that golden era of slowing the decrease in hitting skills appears to be coming to an end. What role performance-enhancing drugs had to play in the rise and fall that was seen from 1990-2012 will only be completely told when players from that time are more forthcoming. PEDs didn't guarantee anything--admitted users like Jose Canseco, Mark McGwire and Ken Caminiti played to ages 36, 37 and 38 respectively, but how much of their punch was due to "punch" perhaps will never be known.

This last chart ties it all together:

Over time, players ages 36 and older have increased, totally expected when factors such as better conditioning, higher salaries and more opportunities allow them to make rosters. If you consider that back in 1901 the average life expectancy was around 50, playing until 35 was almost a luxury. But that orange bulge at the top of the chart seems to be shrinking--the normal declines in performance appear to be returning after a 20-year absence.

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