participants showed up to 40% gains in measured fluid intelligence scores

' * sputters *

What does that even mean? I know what it means for a rock to be 40% heavier than some other rock, or for a car to be travelling 40% faster than some other car, and I know what it means to go from the fiftieth percentile to the ninetieth percentile, but saying that subjects got 40% more items right on some particular test tells me nothing useful; we only care about the test insofar as it gives us evidence about this intelligence-thingy, and the raw score gives me no basis for comparison. Looking at the actual PNAS paper (hoping that I'm competent to read it), it looks like the experimental group saw a gain of 0.65 standard deviations (Cohen's d) on a test of Gf, said figure which actually tells me something---if we assume a Gaussian distribution, then a score in the fiftieth percentile among the untrained would be in the twenty-fifth percentile amongst the trained. (The control group also gained 0.25 standard deviations, probably due to a retest effect.)

Huh. d=0.65 is pretty impressive ...