The Use of Effect Sizes in Music Therapy Research

Music therapy outcome research frequently involves comparisons between groups on continuous scales of psychological constructs. Describing such differences only through statistical tests reduces the existing complexity and creates an artificial and potentially misleading dichotomy. The interpretation of the magnitude of a difference found on a psychological scale is often not straightforward, but can be greatly facilitated and improved by using effect sizes. Cohen's (1988) benchmarks allow for intuitive judgements and enable comparisons between different scales. An example of a study of the effects of music therapy on self-esteem shows how the use of effect sizes can change the interpretation of a research result. Effect sizes have important applications in many fields of music therapy research, including primary studies as well as meta-analyses, and planning of research as well as reporting of research results. Because of their intuitiveness, they may help to bridge the “gap” between research and clinical practice.