AEI and CI

[Flanders]

Since this was started in another thread I thought I'd start a thread here like Diver52 suggested and I just quoted from over there.

I'm kind of wondering how that works for the high dollar sires such as he and American Pharaoh, among others, but I'm not sure there will ever be a way to calculate those figures.
Truly great sires elevate their mares in the long run and help them out produce what their breeding histories might suggest. However, these stallions, as well as Justify, get the best mates with proven records in the breeding shed by breeders who can afford their fees. Is there a way to calculate their AEI with extremely average mares- or is there even a chance that they even get average mares with their stud fees being what they are?
(Not trying to be offensive to anyone, as it has been many years since I've posted on this board, but I've watched with interest many stallions over the years who made their way up the lower breeding ranks and becoming top sires by producing quality foals where their success might not have been predicted. )

Doesn't the "Comparable Index" (CI) try to show what the mares have produced with other stallions? Theoretically a great stallion should have a higher AEI than CI (if I'm understanding correctly) but of course this calculation can also be skewed if a stallion is bred to mares who have already produced major earners, which would make it harder for the stallion to "improve" them.

I see from paging through an old paper Stallion Register that there is a similar set of AEI./CI figures for broodmare sires, but I have no idea how that is calculated. I also noted that a lot of very prominent stallions have LOWER AEI's than CI's, which might play into the thought above.

This probably belongs over in "Breeding and Sales."

This is where having an overall handicapping system, or I guess using a APEX type system, would be useful. It would be informative to have the mare's progeny average rating compared with the offspring of a stallion. However, I think all the numbers are a bit skewed these days as the commercial market has changed how first year stallions have been utilized. Even the non-flashy ones end up with much better books than they would have had even 10-15 years ago because that seems to be what sells these days. For instance, is this a truly bumper first year ( now second year) stallion crop or is it just natural progression of the modern commercial breeding philosophy?

Even when a stallion gets extremely good mares, if he is able to sire good runners it should even out in the end or be close, it just might take a handful of crops to even out. The stallions that do get extremely good books of mares are going to have a harder time having a higher AEI than CI. Even Storm Cat didn't have one because of the mares he was covering.

Bloodhorse has an AEI list that has the CI on it and the Broodmare Sire lists shows AEI/CI as well, though it doesn't say how the Broodmare Sire CI is calculated. Unless its maybe how 1/2 sisters of the broodmares produced. I can't find an answer when searching.

CI does show the average earnings of a foals produced by mares by other stallions. The AEI/CI is tricky. If its a stallion bred to an average book of mares then yes its useful to show they are improving the mares. If its a stallion getting amazing books, it will show that he is either getting super poor results or doing okay. I was going to say it was rare for a top stallion that gets superior books of mares to have a higher AEI than CI but the numbers I provided show that isn't necessarily the case. Let's look at the top 20 active leading sires of 2019 with their AEI/CI. The number after the / is the difference between their AEI/CI.

Stallions who have higher AEI than CI:
Curlin - highest AEI with 2.34 / 0.14
Into Mischief / 0.22
Quality Road - has the biggest difference between AEI/CI / 0.51
Ghostzapper / 0.09
Kitten's Joy / 0.19
Candy Ride / 0.41
Twirling Candy / 0.24
English Channel / 0.13
Lookin at Lucky / 0.07
Munnings / 0.17

Stallions who have lower AEI than CI:
Tapit / -0.01
War Front - has the highest CI / -0.09
Medaglia d'Oro / -0.33
Speightstown / -0.08
Hard Spun / -0.22
Street Sense / -0.23
Uncle Mo / -0.18
The Factor / -0.25
More Than Ready / -0.16
Malibu Moon / -0.11

It's pretty interesting that the list is split evenly 10 with higher AEI, 10 with lower AEI. Even with the lower AEI than CI, its not a huge difference. Also Smart Strike has 3 sons on the higher AEI.
Some other interesting things, Smart Strike has 3 sons on the list of higher AEI.
Candy Ride and his son Twirling Candy both make the higher AEI list.
Bernadini has a massive -1.01 difference.
The young stallion Dialed In is moving his mares up a lot with a difference of +.51.
Declaration of War is another young stallion that is improving his mares.

[ThreeMustangs]

My understanding of broodmare CI is that it’s calculated by the earnings index of those stallions bred to the broodmare sires’ daughters compared to the earnings index of the mares bred by those stallions who are not the broodmare sires’ daughters. I dunno if that makes sense...

[Flanders]

My understanding of broodmare CI is that it’s calculated by the earnings index of those stallions bred to the broodmare sires’ daughters compared to the earnings index of the mares bred by those stallions who are not the broodmare sires’ daughters. I dunno if that makes sense...

Makes sense.

[Diver52]

My head is hurting already.
As I commented in the other thread, I have a paper Stallion Register from about 2016 and it was really surprising how many stallions had a lower AEI than CI. Given how many of those stallions are considered superior, I'm not sure how much value the figures have. Of course the AEI figure itself has been often criticized, and it's a more "Captain Obvious" figure, although influenced by the quality of the mares.

[Flanders]

I don't think it has much value honestly. I mean I guess its a good barometer for if a young stallion is improving his mares but I think breeders would just take note that he is getting good runners. Most of the stallions on the list I put above did improve their first books of mares, except Ghostzapper. In 2020, his AEI was 1.86 and his CI was 3.16. But 10 years later and he is one of the few on that list that does have a positive AEI.

I think the massive books of mares make even the best stallions have books with both spectacular and average mares. They can't find 200+ spectacular mares for all the stallions.

[Green Desert]

Thank you all for the explanations, as well as Flanders for starting it.