Determination of E!ect Size
Studies were categorized as positive or negative
based on statistical superiority to placebo at
endpoint on one or more prospectively defined,
clinician-rated, primary efficacy parameter. Effect
size was also calculated if sufficient information
was available. In some cases this required visual
inspection of a graphical figure to determine an
estimate of the mean value(s). !e Cohen’s d
approach to calculating effect size was used, where
effect size d was defined as the difference between
the two mean changes from baseline (i.e., SJW or
SAM-e change minus the placebo change) divided
by the pooled standard deviation for those mean
changes.71 !e pooled standard deviation was
derived by taking the square root of the mean of
the two squared standard deviations at endpoint. If
variance was presented as standard errors (SE), the
SE was converted to standard deviation to allow for
determination of the effect size.