In case inexact
significant P values (ie, P < .05, P < .01, P < .001) were
reported (n = 37) or when nonsignificant P values were
not reported (ie, ‘‘none significant’’ was stated but no
P value given; n = 20), P values were coded as missing
data. Forty-four studies reported their mean values and
standard deviations or standard errors, and these were
used to calculate the effect sizes. In studies making multiple
comparisons, the largest effect sizes were recorded.