Yes, you can compare, let's say, average income of graduates over a certain period and see that they're bigger for Ivy League graduates But of course averages lie more often than not, and I suspect that, income curves are double peaked for the Ivy League graduates (meaning that'll have the "mere mortal" avg salary and the "exceptionals" forming another peak)
But are the type of people who go to Ivy League schools different from everyone else? I mean: If you're talented enough to get into Harvard, maybe you don't need a Harvard education to succeed in life (for various definitions of "succeed"). I could have gone to an Ivy League school but chose not to. I really can't fathom having a better college & post-college experience than I did...
Anyway, anecdotes are anecdotes.