Investigations of heterogeneity and prediction interval

Heterogeneity was assessed for the individual meta-analyses using the chi squared test and the I ² statistic ²⁹ . Significant heterogeneity was defined as P  < 0.05, with I ²  > 50 % indicating substantial heterogeneity. Further quantification of heterogeneity was categorized based upon I ² with values of 25 %, 50 %, and 75 % indicating low, moderate, and high amounts of heterogeneity, respectively. Given the use of random effects model to estimate average effect, a 95 % prediction interval was calculated to determine the dispersion of effects and clearly illustrate heterogeneity in the calculated effect size ^{30 31 32} .