12.6.2  Re-expressing SMDs using rules of thumb for effect sizes

Rules of thumb exist for interpreting SMDs (or ‘effect sizes’), which have arisen mainly from researchers in the social sciences. One example is as follows: 0.2 represents a small effect, 0.5 a moderate effect, and 0.8 a large effect (Cohen 1988). Variations exist (for example, <0.40 = small, 0.40 to 0.70 = moderate, >0.70 = large).  Review authors might consider including a rule of thumb in the Comments column of a ‘Summary of findings’ table. However, some methodologists believe that such interpretations are problematic because patient importance of a finding is context-dependent and not amenable to generic statements.