The Effects of Age on Hitting by David Luciani Published February 21
The Effects of Age on
by David Luciani
Published February 21, 2002
It's no secret that age
has an effect on hitting but there are plenty of myths still out there.
One popular one is that a hitter's skills peak at age twenty-six or
twenty-seven. While it's true that there are certain skills that peak at
those ages, some skills, such as speed, will peak earlier and other skills, such
as the ability to take walks, peak much later. Even if you don't take
interest in exactly how we can study the effects of age, as many of the less
statistically-inclined readers will not, you can skip to the conclusions at the
end of this essay to see what insights we can gather from the actual data.
Most readers know that I
take great interest in the science of forecasting and though I have written
about age in the past, I have decided in this space to give some insight into
exactly how we can determine the effects of age, how we can't and what the
Firstly, I am not a
believer in those methods that add up the history of baseball, sorted by what
"all twenty-six year olds" have done and what "all twenty seven
years olds" have done and so on, making a futile comparison between the
two. That is a terrible way to analyze the effects of age because many
players leave the league, through retirement or other means, long before their
career is over. If for example, you add up what all thirty-eight year olds
have done, and conclude that all thirty-eight year olds hit .260 over the
history of baseball and all twenty-eight year olds hit .280 over the history of
baseball, you might falsely conclude that a thirty-eight year old loses 20
points off his batting average from ten years earlier.
That's entirely untrue.
Indeed, only a small percentage of twenty-eight year olds manage to remain in
the majors until they are thirty-eight because of their inability to
overcome the effects of age. In fact, most twenty-eight year olds would
evolve into much inferior hitters than the thirty-eight year old population we
can study. We don't have the terrible results they would have accumulated
had they stuck around because they are long since retired.
One way that we can study
the effects of age is somewhat simple but requires a great degree of database
manipulation. Fortunately, I can save you the work because we've already
done it. To study the effects of age, we need to compare players who
played at both ages we are interested in comparing. To accomplish
this, first we took the entire history of baseball and neutralized each year's
statistics for the effects of the era and, where data was available, the effects
of the park.
For example, we start with
all hitters who played when they were both 18 and 19 years of age. If they
didn't play at both ages, then obviously we can't use them to consider the
difference in their performance. Secondly, we neutralize the plate
appearances so that we scale down the year in which the player appeared more to
the amount of time in the year in which he played less. For example, if a
player had 30 hits in 100 plate appearances when he was 18 years old and he had
50 hits in 200 plate appearances when he was 19 years old, we scale down the 50
hits to the number it pro-rates to over 100 plate appearances. Once we
have these totals, we can add up all the reduced results and plate appearances
over both years to find out the total effect of age on categories. I've
summarized and simplified an entire chapter's worth of analysis into one
paragraph here so if you don't follow the method, we will return to this in
future essays. I am more interested in presenting some of the results at
We took the entire history
of baseball, with adjustments for era, league and park (where possible) and
analyzed the effects of age on every category of performance. When the
analysis was finished, and our first version of this was completed in 1994, the
curves were so extraordinarily smooth that it seemed clear that we had stumbled
onto some hidden equations of nature. Since 1994, we have continued to add
the new data into the model though it has not significantly changed any
equation. We do keep updating it, just in case something new should
appear. We use these equations, in combination with many other factors,
when making the forecasts you see online.
Let's start by looking at
the graph for hits per plate appearance (not to be confused with the more
popular hits per at bats):
Now, I have not altered
the graph in any way and these are the real results we have from our post-2001
analysis. Any result above 1 means that a player's ability to get hits,
per plate appearance, improves relative to the year before. Any result
below that means that he declines. As you can see, a player's skill up
until about the age of 25 sees his total number of hits per plate appearance
improving relative to the year earlier. As you can see, he improves more
between the ages of 19 and 20 than he does between the ages of 24 and 25 but in
both cases, he is still improving. By the time he is 40, he would be
facing an annual decline of about 5-10% per year on hits per plate appearance
compared to the year before, which is why few last that long because losing
5-10% of your hits over the span of a few years will quickly destroy your
Remember of course that
this is the average hitter. A small percentage of hitters will
dramatically improve/decline beyond expectations and a small percentage will
actually do the opposite. The point here is to study the typical expected
effects of age on a hitter. The reason I observed above how a hitter does
per plate appearance rather than by at bat is because at bats per plate
appearance are also affected by age, actually declining until the player is
about 29 or 30, mostly because he gets better and better at taking walks as he
gets older and walks are a rare skill where a player continues his improvement
into his mid thirties, largely because taking walks is not as much a physical
skill as it is one of experience.
So having said that, let's
study an untypical 18-year-old who hits .290 over 500 major league at bats.
It's rare for a player so young to do something like that but let's take a look
at this hypothetical situation. The at bats should decrease slightly as he
gets older, the hits increase as above, and this is the expectation for the
player. Notice just how perfect the line comes out, without any smoothing.
This is using the chart results from our raw study on the effects of age on
batting average and the line is fantastically smooth, so smooth that we can be
fairly certain that our analysis has not yielded coincidental results:
As you can see, our .290
18-year-old has done something extraordinary and according to even the average
expectations, he should quickly develop into a .310-.315 hitter over the next
several years. He should stay above .300 until around thirty and then see
a steady decline. In the unlikely event he were to still be playing into
his late thirties, by the age of thirty-eight he becomes just a .235 hitter.
By his early forties, our one-time batting title contender, probably long
retired by now, should be expected to be just a .188 hitter.
I present this graph not
to reveal the entire study on the effects of age, though I will talk much more
about this analysis over the season and will focus on other categories such as
power and speed. The point here is to demonstrate why a .290 18-year-old
should be expected to become better than a .300 hitting 21-year-old. Let's
take a look at a .300 hitting 21-year-old, using our same age effects
Our .300 hitting
21-year-old actually should not get much better average-wise, though he still
has some expected improvement. This hitter, by the time he is twenty-four
years old, should be peaking around .305-.310. Beyond that, his decline
below .300 will come at the young age of just twenty-seven and if he is somehow
still playing when he's into his forties, he should be expected to become a .183
hitter by the age of 42. In fact, if our .290 18-year-old and our .300
21-year-old are playing at the same time, our .290 18-year-old will move ahead
of our .300 hitter about two or three years from now.
Now the problem with any
analysis such as this is that we're considering averages and as with any set of
averages, there is a wide deviation in actual, eventual performance. Some
great players in modern times have exceeded the expectations that age data would
otherwise imply (consider Roberto Alomar) and others have fallen short (Tony
Batista for example).
One result from our
analysis is that we are able to say, with some degree of certainty, when skills
actually peak, on average. Please note that these ages do not mean that a
player should achieve a career-high in these categories. It means that the
player's skill per plate appearance in that category should actually peak at
this age if they were to still be playing, but the best base-stealers will
achieve career-highs much later than their peak speed because they will play
more when they are older.
Whether you agree or
disagree with the analysis, these are rooted in fact and I present the results
only for your entertainment. None of these conclusions are rooted in what
I or other people believe or say and they are all simply the result of
calculations. Accept them then for what they are, the results of a
numerical analysis of every hitter in baseball history:
A hitter's batting
average ability typically should peak at twenty-four.
A hitter's ability to
to hit doubles typically should peak at twenty-four.
A hitter's ability to
hit triples typically should peak at twenty-one (meaning most hitters
experience their triples peak while still in the minors and thus achieve
their eventual major league career high in triples much later than the peak
of the same skill).
A hitter's home run
skill should typically peak at twenty-six (which may back up the popular
"26 with experience" theory).
A hitter's ability to
take walks typically should peak at thirty-five (really!).
A hitter's ability to
avoid striking out typically should peak at twenty-nine.
A hitter's ability to
steal bases typically should peak at twenty-three.
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