standardised mean difference (SMD)

Alternative spelling: standardized mean difference (SMD) The difference between two means, divided by an estimate of the within-group standard deviation. Note: When a continuous variable (such as pain) is measured in a variety of ways across studies (using different scales), it may prove impossible to compare or combine the study results in a meta-analysis. If the effects are expressed as a standardised value, the results can be combined, since they are no longer expressed as units of measurement. Standardised mean differences are sometimes referred to as a “d index.”* *Concept introduced by J. Cohen (1988).

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