In his classic article on the fallacy of the null hypothesis in soft psychology [J. Consult. Clin. Psychol. 46 (1978)], Paul Meehl claimed that, in nonexperimental settings, the probability of rejecting the null hypothesis of nil group differences in favor of a directional alternative was 0.50-a value that is an order of magnitude higher than the customary Type I error rate. In a series of real data simulations, using Minnesota Multiphasic Personality Inventory-Revised (MMPI-2) data collected from more than 80,000 individuals, I found strong support for Meehl's claim.
- Null hypothesis
- Soft psychology