Bud Norris' injury probabilities: The importance of context

The offseason is over.  Hallelujah.  With pitchers and catchers beginning their first workouts under Astros manager Brad Mills, there are few questions left for us to ponder because answers are on their way.  However, the two most lingering questions of the offseason (will Bud Norris stay healthy and can Tommy Manzella play defense) still have me nervous.  

Thankfully, the Verducci Effect has been hot lately.  So hot that there have been three statistical inquiries into its merits and a whole host of discussion surrounding all of it.  With Bud Norris listed as the second candidate on Verducci's annual list, this meme has become fascinating.  There have been interesting takes and findings on what the actual effect the Verducci effect (an increase of 30 innings or more over the career high of a pitcher under 26) might wrought for his future.  Since Norris is a leading candidate, let's delve into what those takes and findings might imply for Bud's 2010 campaign.

To quickly sum up the Verducci Effect for those not in the know, Rick Peterson, at the time that he was the A's pitching coach, determined that the most reliable indicator for injury was too many innings too soon.  Since baseball writer Tom Verducci caught wind of this, he has tracked pitchers with the aforementioned qualifications and people have paid attention. The name itself, however, was coined by Dr. Will Carroll of Baseball Prospectus, who also saw the pattern and correctly named it after its biggest proponent.  Until the injury database was released a few days ago, there hadn't been an all encompassing, easily utilized data set to test the Verducci Effect.  

Problem solved.

The first study that I stumbled upon was by Baseball Analysts' Jeremy Greenhouse.  Using Pitch/fx data, combined with the injury data, Greenhouse tested the correlation between performance indicators, usage patterns and injuries. His results are far more nuanced than the summary I'm about to provide, but this succinctly wraps it up:

The Verducci Effect, like most everything else I tested, is not significant in predicting future injuries. Injuries are hard enough to predict as is, and there's certainly no straightforward rule of thumb. A high workload does coincide with a trip to the DL the following year, though the causative effect may be that pitchers who throw a lot of pitches have more opportunities to get injured, rather than the pitches placing more stress on their arms.

Essentially, Greenhouse found no real indication that the Verducci Effect is useful for predicting injuries. And, even if it would have been, it wouldn't have been the reasons for which the Verducci Effect has become famous.

JC Bradbury has dedicated two efforts to the Verducci Effect as well.  In his first effort, Bradbury tested the literal claims of the Verducci Effect (that a pitcher will become less effectived/injured), and found this:

If you increased your workload by more than 30 innings in the preceding season and are under the age of 26, then we should expect to see a decline in innings pitched and ERA. However, it turns out that this is not the case. In terms of workload, Verducci Effect pitchers actually increased their innings pitched between 19 to 22 innings. In terms of performance quality, pitcher ERAs declined by an average of 0.1 runs; however, the effect was not statistically significant, which means it’s probably best to say there is no effect.

His second effort utilized the injury database and simply looked at the predictive value of the Verducci Effect on trips to/days on the DL.  He, again, found no statistical support for the Verducci Effect's hypothesis.

As I mentioned at the outset, the value of this discussion is that Bud Norris is a Verducci candidate.  So what does any of this tell us about Norris' Verducci-osity? Not a lot. The statistical inquiries into the the Verducci Effect's validity say that it tells us very little.  We know that we shouldn't necessarily condemn Norris to a season full of ineffective pitching, or one spent on the DL.  But what else?

I think that what the Verducci Effect can't tell us is much more than we could hope for from the hypothesis itself.  If the various statistical inquiries cannot find a reliable correlate in the injury database from seemingly obvious variables that should predict injury (thresholds of usage, fastball velocity, etc.), then there is no correlate for the sample (either that, or we just don't have a way to measure whatever it is just yet...I'll table that thought).

Obvious, I know. To me, that was a refreshing of the intuition.  To quote Greenhouse again, "there is no rule of thumb."  When I wrote about Bud Norris' yellow flag from Will Carroll's Health Matrix, I referenced Norris' PAP and the inverted-W to Carroll when asking for a comment.  In his response, he chided me for pitching those "facts" to him as though they constituted legitimate herrings for Norris' health.  Although some of his response was off the record, essentially he spoke about the very individual nature of injury.

With this week's focus on the failings of the Verducci Effect from a statistical standpoint, hopefully more emphasis will be put on determining how to go about understanding injury on a micro-level, and macro-level attempts to predict injury gain less credence.  Until pitch/fx modeling, combined with bio-mechanics, and lord-knowns what else allow for this to be easily done, we're still left in the dark.

What do we make of Norris' 78.2 IP increase in 2009?

We know that it was a substantial increase, in a year following an elbow injury, but that Norris' MLB inninngs weren't high on the stress scale.  Referring back to Greenhouse's conclusion, we know that the increase alone provides a greater sample space for Norris to have inflicted damage upon himself.  Thus, we can conclude that 2/3 of the known facts about Norris' 2009 campaign are negative.  We know that the information Will Carroll pays attention to has flagged Bud Norris a strong candidate to wind up on the DL, too.

What we don't know is just what kind of adjustments Norris might have made after his 2008 elbow injury.  We also don't know how scrutinized Norris' every pitch has been by the organization.  All we can really do is trust that they knew about the increased chance of Norris injuring himself through his increased sample space because we also know that the Astros, as an organization, have been remarkably good at keeping players healthy.  If they kept all the critical pieces of context in play, perhaps we should trust that they made an informed decision.

Then again...there is that whole thing about Norris' arm being too fatigued to finish out September that can be worrisome.