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Old 02-22-2005, 09:45 AM
js_africanus js_africanus is offline
Join Date: Nov 2002
Location: Small City, Michigan
Posts: 5,162
In my psychology classes, regression toward the mean was explained this way: if you do really well on a on a test, i.e. better than you normally do, you probably won't do as well on the next one. That doesn't mean that you are slipping, it just means that if you're far from your average on one test, you'll be closer to your average on the next.

Suppose instead one particular student scores much more highly on a test than the class does as an average. You shouldn't use regression toward the mean to conclude that she will score more closely to the class average on the next test, because she may be a better student. Her personal average, in that case, would be higher than the class average.

I once saw Gould on C-SPAN talking about the OP's question, sort of. Baseball is less likely to be producing uberhigh batting averages than it had earlier in the century. Does this imply that baseball players aren't as good as they were in the past? No, it is a reflection of the fact that better scouting, grooming, and training is reducing the variation between players by bringing more people nearer the limit of human ability.

Because we are nearer to the wall of human ability there will be fewer outliers on the really-good end of the batting scale, therefore we cannot conclude that players aren't as good generally because we see fewer .400 batters. (Or whatever average; I don't know baseball.)

As nutrition and education become more universally good (ugh, poor writing!), I'd imagine that we may see fewer exceptionally smart people because we are bringing everybody closer to the upper limit of human intelligence.

At least, that's how I understood it from what he said....