2.1.6 Statistical analysis
In this study, since the outcome indicators were continuous variables,
the effect sizes were combined using the standardized mean difference
(SMD) with 95% confidence intervals and the random effects model was
used to pool effect size. A significant difference between the
experimental and control groups was indicated by a P-value <
0.05. To evaluate heterogeneity, the I-square (I2) was
used, and values of I2 ≤ 50% indicated that the
included studies were homogeneous. If I2> 50%, it indicated that the included studies existed
heterogeneity, and subgroup analyses were conducted to explore the
sources of heterogeneity. The combined effect sizes were then combined
using random effects models.