Comment by gwern
6 years ago
> Finally, I didn't read through the whole thing. Does he claim to have found an exception to this rule at any point?
Oakes 1975 points out that explicit randomized experiments, which test a useless intervention such as school reform, can be exceptions. (Oakes might not be quite right here, since surely even useless interventions have some non-zero effect, if only by wasting peoples' time & effort, but you might say that the 'crud factor' is vastly smaller in randomized experiments than in correlational data, which is a point worth noting.)
Thanks,
How about this "fact": The fact that these variables are all typically linear or additive?
That is simply a corollary of the fact that Pearson's r and regressions are usually linear/additive, and things like Meehl's demonstration wouldn't work if they weren't. You'd just calculate all the pairwise correlations and get nothing if they were solely totally nonlinear/interactions. (In which case you'd have a hard time proving they were related at all.)
> You'd just calculate all the pairwise correlations and get nothing if they were solely totally nonlinear/interactions.
I don't believe this. Most nonlinear correlations also show up as non-zero (linear) correlation coefficients. There are really only a couple pathological cases I can think of where it would not happen.