Effect-Size Calculation
Primary analyses were conducted through the Comprehensive
Meta-Analysis software package (BioStat, Englewood, New Jersey),
using Hedges’s (1982) formula for calculating effect size: g
(MPost MPre)/SDP , where MPre is the preintervention mean task performance,
MPost is the postintervention mean, and SDP is the pooled standard
deviation. All effect sizes were weighted by Hedges’s sample-size correction:
c * g, where c 1 3/(4m – 9), and m 2N 2. Effect
sizes were coded such that positive numbers always reflected improvements
in performance, and negative numbers reflected deterioration in
performance.
Codi