Another criticism is that meta-analyses mix studies of varying methodological quality, or the
‘garbage in, garbage out’ problem. We have noted that measures of methodological quality can be
used as eligibility criteria to restrict studies to only those of high quality or as a moderator variable
to examine the relationship between methodological quality and effect sizes. Nevertheless, a reader
of a meta-analytic report needs to make a determination about the extent to which methodological
features, particularly those not examined as moderator variables, might account for some of the
observed variation in effect sizes.