Belmont over the last 2700 races gives 33% favorites and Ascot over about the same amount gives 32%.

The size of the fields no doubt determines the percentage of winners to a large degree.
Now Kojonup, where we're all headed tomorrow has a return of 47.61% favorites over the last 42 races in 7 years or so.

KV

P.S. But then if you'd bet the first horse in alphabetical order at kojonup you'd have scored 35% winners and made a 6% profit. Last horse in alpha order only 21% winners and a loss of 40%.

I think some people on this forum could base a system around that :-)