I have a share in Dan Uggla – one I acquired earlier this year in an attempt to boost my power numbers in the ottoneu FanGraphs Experts League. The results have been mixed, and missing Uggla for at least a couple weeks now won’t help. But Uggla is not overly expensive in that league ($14) and a boost from Lasik could make him a keeper in the off-season.
Before getting too far into this, I should note that I am by no means and medical (or statistical) researcher, and that my writing today is more meant to raise questions than to claim that the study in question is flawed. But I saw three potential issues in what I read, and what I found subsequently gave me some hope that Uggla could come back better than he was before.* Sample size is clearly an issue here, but since the study mentioned that directly and since there isn’t much we can do to solve this, we’ll focus on the others.
Issue 1: Age
The study does not directly consider the impact of age on the players in question. The 12 players whose stats are outlined in the study had an average age of 30.1 at the time of the surgery, but the range is from 24 to 38. The fact that Larry Walker saw a decrease in production from his age 37 to age 38 season may not be all that surprising. Same for Wally Joyner in his after 35 and 36 seasons.
Issue 2: League Context
This study looks at raw hitting data, rather than adjusting for league context. A number of these surgeries happened 1999 and 2000, and looking at 1-2 years before that vs. 1-2 years after may not be the best sample if you are not going to adjust for context.
Issue 3:Two Year Periods
While I understand the sample size issue with only taking one year before and one year after, anyone who wears glasses knows that a year can make a big difference in your vision. A player who was an all-star in Year 1 with great vision, could have vision issues in Year 2, be back to himself thanks to surgery in Year 3, and then fall off in Year 4 simply due to the passage of time. We don’t know enough about these players to say that this is the case, but I am not sure that it is all that meaningful to say that a 33 year old Bernie Williams, two years post-surgery, was worse than a 29 year old Bernie Williams who may have had great vision.
For my own mini-study, I a) added players ages to my table, b) removed Todd Dunwoody, whose career seemed to not justify being in this group, and c) used wRC+ to adjust for league context. The table is below:
|Player||Age at Surgery||2 Yrs Prior||Yr Prior||Yr After||2 Yrs After|
The blank spots are years in which guys did not play or did not accrue more than 200 PA.
The first thing that jumps out is that league context offensive contribution went up by a wRC+ of 11.7 in the year after the player had the surgery. That’s no joke. In 2013 terms, this is taking Nate McLouth, Albert Pujols, Mike Napoli or Eric Hosmer (interesting group with wRC+ of 111) and turning them into Nelson Cruz, Billy Butler or Jean Segura (wRC+ of 123). It is a sizable change. They were, on average, still better in year four than in year two.
We can also break this down further. There are three players 25 or 26 years old, six who are 30-32 (Uggla, by the way, is 33), and two who are 36+. The two senior-most gentlemen went from a 138.5 average wRC+ in Year Two to 113.5 in Year Three, which is no surprise given their age. Everyone else went from 104.7 to 124.8 and stayed at 113.6 in year four.
But maybe counting three mid-twenties guys isn’t fair either. Only focusing on the players roughly in Uggla’s age range (30-32), the six players presented went from a 104 wRC+ the year before surgery to 133.2 the year after. Greg Vaughn drove much of this himself, but Bernard Gilkey saw a big jump, too.
All in all, the sample size is still small and the data is still rough, but when we account for age and league context, the picture gets quite a bit rosier. Maybe the way I am looking at the data suggests I need the surgery more than Uggla does, but I am not ruling out the possibility that we will see noticeable gains once Uggla can see. I’ll be watching him closely down the stretch and if he seems to have a better eye at the plate, seems to be making more contact, and sees an uptick in his production, I’ll be accounting for that in my valuation of him for 2014.
*Note that I mean before the surgery, not before the Marlins traded him and he went from star to just really good hitter.
Chad Young is a product manager at Amazon by day and a baseball writer (RotoGraphs, Let's Go Tribe), sports fan and digital enthusiast at all times. Follow him on Twitter @chadyoung.