[Rupert Pupkin]

Originally Posted by GenuineRisk

I don't know this is true until I see the actual stats.

What has remained quite consistent, it seems, is that it's to a Preakness starter's advantage to have run in the Derby. Here's an article from 2014 about it:

https://thoroughbredracing.com/artic...ners-preakness

And one from 1998. La plus ça change...

http://articles.latimes.com/1998/may/14/sports/sp-49712

That doesn't prove causality by any means. The reason Kentucky Derby horses do well in the Preakness is because the best three year olds run in the Kentucky Derby. Sure there is the rare occasion where one of the best three year olds doesn't get into the Derby or has to skip the Derby for whatever reason. But in the vast majority of cases the best 3 year olds run in the Derby. So they don't win the Preakness because they ran in the Derby. They win the Preakness because they're the best horses.