2.6. Data synthesis and statistical analysis
The fixed-effects model and the random-effects model are based on
different assumptions. The results of meta-analysis using fixed-effect
models are limited to specific populations. As we cannot expect these
studies included in the research to show the same widespread impact; the
fact that the studies were conducted under different conditions (i.e.,
geography, dosage, measurement, etc.) could indispensably cause
differences among the results. Thus, in the identification of effect
sizes during the present meta-analytical processes, analyses were
conducted according to the random effects model31.
We
computed standardized mean differences (SMD) with 95% confidence
intervals(95%CI)27 to estimate effect sizes for
continuous outcomes. Besides,we use stratified analysis to explore
subgroup analysis. Data were further analyzed by using Stata 12.0,
Comprehensive Meta-Analysis 3.0,
and
Review Manager 5.4.