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Revisiting 2011 SP DL Projections

Last off season, I looked at the chances of a SP going on the DL. I have finally had time to go back and look at how my predictions fared.

The predictions used logistic regression to find the percentage chance that a pitcher would end up on the DL. I used age, games started in the previous 3 years and how many of the previous 3 years did the pitcher go on the DL. The equation I ended up with was:

1/(1+e^(-z))
where:
z = (.2209)(Years with Trips to DL)+(-0.0040)(GS in last 3 year)+(0.0509)(Age in previous season)-1.7692

Using the equation, I projected the chance that a starter would go on the DL and here is a list of those projections.

To see how the projections stood up, I examined the 25 most and least likely players to end up on the DL. I look to see if they were on the DL in 2011 and what was their chance of going on the DL. I added up the individual percentage chances and figured out the percentage of pitchers that actually went on the DL. I removed any pitchers that did no pitch in 2011 because of retirement like Andy Pettitte.

The 25 players most likely to end up on the DL values ranged from 43.5% (Roy Halladay) to 55.1% (Daisuke Matsuzaka). Of the 25 players, 12 went on the DL in 2011, or 48%. The average percentage chance predicted that 12.2 players or 49% would make the DL. The model held pretty good. This group of players had an average age of 31 years old, pitched in only 65 games over the past 3 season and went on the DL 1.75 times over that time frame.

The pitchers with less of chance to end up the DL ranged in value from 27.3% (Clayton Kershaw) to 32.7% (Paul Maholm). Of the 25 pitchers, 9 went on the DL in 2011, or 36%. The average percentage chance predicted that 7.75 pitchers or 31% would end up on the DL. The final prediction for these pitchers was not as good as the DL prone pitchers, but close. The pitcher’s average age was 25 years old, pitched in 79 games in the previous 3 season and has never been on the DL.

The key is that some pitchers are historically more likely to go on the DL than others. The percentage chance can be to the tune of almost 30% ( Daisuke Matsuzaka at 55% vs. Clayton Kershaw at 27%). An older, DL prone pitching staff will need to have several more options ready when its starters go on the DL than a staff of young healthier pitchers.