Evidence from several nations indicates that performance on mental ability tests is rising from one generation to the next, and that this “Flynn effect” has been operative for more than a century. No satisfactory explanation has been found. Nevertheless, the phenomenon has important implications for clinical utilization of IQ tests. This article summarizes the empirical basis of the Flynn effect, arguments about the nature of the skill that is increasing, and proposed explanations for the cause of the increase. Ramifications for clinical neuropsychology are discussed, and some of the broader implications for psychology and society are noted.
Among other things, Hiscock notes that Flynn and others have found the Flynn effect, and the related occasional re-norming of IQ scores, to cause jumps in the number of people classified as mentally retarded (conventionally, an IQ of 70, which is two standard deviations below the mean if the mean is scaled at 100). When they rescale the tests, the proportion of people labeled “retarded” jumps up. Seems like a natural experiment that might be a good opportunity to study effects of classifying people in this way on the margin. If the renorming is done differently in different states or countries, this would provide more opportunity for identifying treatment effects.
See here for a discussion of Flynn’s thought on why meritocracy is logically impossible (also here for related thoughts).