A few weeks ago I wrote about an idea I had for calculating AEI and CI by crop. It turns out that one part of what I wrote was accurate - things are rarely as straightforward as they seem in statistical analysis!
The reason I want to calculate AEI and CI by crop is to see what kind of crop to crop correlation there is for AEI and AEI/CI for sires and evaluate the value of these measures as predictive statistics.
It does look like there's a way to do this, but it's more complicted than I had anticipated. First, I'll need to calculate my own version of AEI by crop based on following a group of stallions data through The Bloodhorse's 'Leading First Crop', 'Leading Second Crop', 'Leading Third Crop' lists. Basically, I'll figure out average earnings per starter in each of those crops.
Then I'll need to figure out the CI for each crop for those sires. I should be able to do this by using the following formula:
Crop CI = ((Total CI * Total Starters) – (Previous Year’s Total CI * Previous Year’s Total Career Starters))/Starters In Crop
Basically I'll be looking at changes in career CI from year to year, and based on the number of starters in this crop compared to the number of career starters the sire has had, figuring out what the CI for the current crop would have had to be to impact the career CI by the amount it changed by.