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Wednesday, July 07, 2010
Pitcher strikeout spikes: what to expect
Eric does some great work:
All told, there were a whopping 21 pitchers with three years on both sides of the spike that also met the criteria of having a pre-average between 5.5 and 7.5, with 100 or more innings in the three years leading up to the spike, and who also saw their K/9 jump by at least 1.75 strikeouts.... Overall, the 21 pitchers averaged a 6.24 K/9 in the three years leading up to the spike, an 8.65 K/9 in the year of the spike, and a 7.34 K/9 in the three years following.
What would Marcel have expected? Let’s see, if we weight it as 3:2:1:0, that would mean the “year of the spike” gets a weight of “3”, the 3 years preceding would get 2+1+0, or a weight of 3. Meaning, a simple average of the two numbers Eric presents: 6.24, 8.65 = 7.45, which compares favorably to the 7.34 actual. Basically, there’s nothing special here in terms of “new established level of performance” from banner seasons… just another data point for us to weight more because it happens more recently.
Note1: I’d use PA, not IP, but that’s what the data that was presented.
Note2: For K rates, Eric correctly notes that they are more stabilizing, so I would weight it more like 5:2:1, so more like say two-thirds the spike season, and one-third the prior seasons.
Note3: Don’t forget regression.
Note4: Putting the three notes together, the 6.24 K per 9 IP is probably about 16% K per PA, and 8.65 K per 9 IP is probably 23%. Let’s say league average is 15%. Taking 60% of 23% and 30% of 16% and 10% of 15%, and we get 20.1%, which we work backwards to get to 7.57 K per 9 IP.
Note5: Marcel is vindicated.
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