Method
A fixed-effects model meta-analysis (Hedges & Vevea, 1998) was conducted to test the
preceding hypotheses.1 Meta-analysis is an approach for aggregating the results from
a body of research (Hedges & Olkin, 1985; Hunter, Schmidt, & Jackson, 1982; Lipsey
& Wilson, 2001). Meta-analysis serves two important functions by making it possible to (a) compute a weighted mean effect size from a sample of cases, and (b) test
moderating variables that may explain inconsistent findings in a body of research. All
effects in this manuscript are reported in the form of d, which represents the
difference between the inoculation treatment and control group means in standard
score form.