MISUSE OF STATISTICAL TESTS IN 3 DECADES OF PSYCHOTHERAPY-RESEARCH

This article reviews the misuse of statistical tests in psychotherapy research studies published in the Journal of Consulting and Clinical P sychology in the years 1967-1968, 1977-1978, and 1987-1988. it focuses on 3 major problems in statistical practice: inappropriate uses of nu ll hypothesis tests and p values, neglect of effect size, and inflatio n of Type I error rate. The impressive frequency of these problems is documented, and changes in statistical practices over the past 3 decad es are interpreted in light of trends in psychotherapy research. The a rticle concludes with practical suggestions for rational application o f statistical tests.