Stephen Strasburg and the Verducci Effect

I sometimes think some ideas are firmly illustrated to be wrong and then become surprised when I see that there are back wellings where the idea still holds.  One of these ideas is the Verducci Effect.  The Verducci Effect specifically is about how with pitchers 25 years old and younger who throw more than 30 IP in comparison to their previous year pitcher will be at a greater risk for injury.  The term is often broadened to mean really anything to do with giving a young pitcher too much work before he gets older.  The idea had a lot of traction at first as it made some logical sense.  Young arms are growing arms and young arms are less experienced arms.  Like anyone at the gym or running, you slowly build up your strength or stamina over time with increasingly great feats.  This makes sense to us.

However, time and time again, the Verducci Effect has been shown to not be real at all even though he delivers a column or two on it every year (though now it looks like he is transitioning over to injured closer stories).  The earliest study I can find is from David Gassko in 2006 that found "overworked" pitchers appeared to pitch more, not less, innings the next year.  Jeremy Greenhouse wrote a column on injuries and the Effect...once again finding nothing to the notion.  I am sure there are many, many other articles by amazing writers who went on to be employed by Major League Baseball franchises.

That said...the Nationals claim they have evidence that shows in their favor the need to end Stephen Strasburg's season even though he is one of their best arms and they will be entering the playoffs.  From my qualitative perspective, it has seemed that this application of the Effect pleases Tom Verducci.  I figured to give the idea another look and measure the general idea in a slightly different (but incredibly simple) way.  Are the Nats using data over several years, not just one?  They have control of Strasburg's rights in 2013, 2014, and 2015.  In a marathon sense, keeping him healthy over that period is more important than the result of four games in September and, arguably, a couple games in October.  In a Keep-Your-Eyes-on-the-Prize sense, well, he should be pitching.

To test this, I took every pitcher from 1998 to 2007 (a ten year period) who threw more than 140 IP t age 23 and within his first three years of pitching at the MLB level.  I then proceeded to sub-divide these players into 20 IP allotments.  For instance, 140-159, 160-179, 180-199, 200-219, and 220+.  I then individually compared their current season to the accumulation of their next three seasons.  I compared how many innings they pitched as well as creating a metric for this study, vFIP.  To measure vFIP, you divide a pitcher's age 23 FIP by the next three year accumulative FIP.  A vFIP over 100 shows improvement and vice versa.

The first thing to look at would be injuries.  Half of the ten pitchers in the 140-159 class suffered injuries over the next five years (Ricky Nolasco, Josh Beckett, Roy Oswalt, Daniel Cabrera, and Ken Cloude).  This sounds like a great deal of loss, but every innings group roughly had the same injury effect rate, which would agree with previous studies. 

Perhaps better would be to compare actual work loads over the age 24 to 26 seasons.  In terms of innings pitched, there was no significant difference between the 140-159 group and the 160-179 (p=0.78) and 180-199 (p=0.66) groups.  However, significant differences were found between that group and pitchers who threw more than 200 innings (0.03 and 0.04, respectively).

140	160	180	200	220
135	128.1	147.1	191.1	194

There is likely to be a selection bias in play here as if a pitcher was given the opportunity to throw 200 innings in a season then he is likely to be a very good pitcher (or considered to be one) and earn or be given the opportunity to pitch a great deal over the next three seasons.  At the very least, it appears that pitching fewer than 200 innings changes what will happen much at all.

The final aspect to look at is performance.  This is where I will break out the vFIP metric and here is the data set:

140	160	180	200	220
123	118	104	100	108
111	83	103	83	92
87	102	93	113	87
76	104	100	96	122
131	82	98	106	65
120	106	124	83	98
99	90	98	92
130	101	86	114
96	85	94	105
96	129	80
116	106	111
	105
	82

The groups are not significantly different from each other.  However, there appears to be a slight improvement in performance from the 140-159 group.  Again, this is not significant and likely requires a larger data set to see if this trend can be more firmly established, but the 140-159 pitchers improved their performance by 16% as a group.  The other four groups were consistent with improvement ranged from 1 to 3 % better than their age 23 seasons. 

Again, there may be some selection bias in these groupings because if you are tossing over 200 innings then you have probably pitched very well and it will be difficult to improve upon that.  Here are the raw FIPs for the groups.

	140	160	180	200	220
Age 23	4.64	4.73	4.4	4.24	4.18
24-26	4.01	4.65	4.28	4.17	4.16

The data suggests that the 140-159 group pitchers saw great improvement in their performances.  However, I would temper those differences with the idea that perhaps a pitcher who throws 140-159 innings at age 23 and proceeds to do poorly is more likely to be replaced in the rotation than a pitcher who tosses more innings.  There may be a prejudice that benefits pitchers who threw more innings during their age 23 season.

That all said, I am not sure how this informs us about Stephen Strasburg.  There is no evidence from the above methodology that injury rates decrease.  It appears that pitchers who log in more innings during their age 23 season wind up throwing more innings in the future at about the same level of performance.  Pitchers who are worked for 140-159 MLB innings tend to show improvement as a group in terms of performance, but not in innings pitched.  This may be the result of less desirable pitchers being able to be discarded more easily when they have less of a track record.