I think it's actually supposed to be quite difficult to see who is above average. At least in "A Random Walk Down Wall Street", they cite some statistics about

I think it's actually supposed to be quite difficult to see who is above average. At least in "A Random Walk Down Wall Street", they cite some statistics about how only 20% (?) of managers beat the market over a period of time, but it isn't the same people who do it over different periods of time.