I think it's a hard question to answer, because you might have program A which has a hundred affiliates mostly promoting on TGP/MGP and similar, and program B which has affiliates promoting mostly with blogs, freesites, etc.

Program A might have average conversion of 1:2000 and program B might have 1:300

Then again, if a program has a $1 trial, it's very possible they might have 1:50 conversion.