The account taken of statistical power in research published in the British Journal of Psychology

Since approximately 1925, researchers in psychology have evaluated their hypotheses against the probability of making a Type I error. Attempts to persuade researchers to augment this information, with details such as effect size and confidence intervals, and in particular to take the probability of a Type II error into account, have largely been ignored. The present paper reviews the degree to which statistical power has been explicitly considered in papers published in the British Journal of Psychology in 1993 and 1994. It summarizes the power for small, medium and large effect sizes for 54 papers, based on the sample sizes which were employed. The analysis confirms that the power of statistical tests is not taken into account by researchers and that, accordingly, they continue to run a high risk of rejecting their research hypotheses.