Statistical power and research in occupational therapy", Occupational Therapy

The rationale ofstatistical hypothesis testing is reviewed, and the concepts ofexperimental error andpower are introduced and discussed. A post hoc power analysis of 205 statistical tests from 22 articles reporting occupational therapy research is presented. The effect sizes andpower coefficients for each ofthe statistical tests reviewed were analyzed, and the evalua-tion revealed a significant dIfference in power values basedon effect-size calculations: Studies reporting small and medium effect sizes were associated with low power and were subject to a high probabIlity of Type II experimental error. The power of the tests reviewed and the estimated Type II error rates were shown to varysignificantly for small, medium, and large effects. This was not true for Type I errorrates, which re-mained constant for all effect sizes. The implications of the findings and the importance ofpre-experimentalpower eval-uations for fields such as occupational therapy, where research endeavors frequently reveal small effects, are discussed. Kenneth Ottenbacher, MS, OTR, is a doctoral student at the University o