from Amazon
Friday, March 14, 2008
Catcher Blocks
Goalies have save percentages. Now, catchers have block percentage. How real is it? Varitek and Ausmus’s performances are 4 standard deviation from the mean (on the good side), while IRod is 4 SD on the bad side. The standard deviation of all these z-scores is 1.93. This would imply a year-to-year correlation of r=1-1/1.93^2=.73. (If it was not a skill at all, then the SD of the z-scores would have been 1.00.)
The average number of opps was 190 opps. This would imply an r=.50 level at opps = 70 balls in the dirt. (That is, 190 divided by 190+70 equals 0.73.) Dan didn’t provide the sample number of innings for each catcher. If he can tell us that, we can figure out how many games 70 balls in the dirt represents.