Читать книгу Health Psychology - Michael Murray - Страница 119

An effect size is the strength of the association between study variables and outcome as measured by an observed difference or correlation. Cohen’s d and Person’s r are the most popular indices of effect size in psychological studies. The effect size is a measure of the importance of an effect rather than its statistical significance. Effect sizes are used in meta-analysis as a means of measuring the magnitude of the results obtained over different studies. Effect size is related to the power of a study to detect a difference that really exists. A weak study cannot detect a real difference because it has samples that are too small relative to the magnitude of the difference that exists, a common problem in psychology. It is estimated that 60–70% of published studies in psychology journals lack sufficient power to obtain statistical significance.