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Forest plot for subgroup analysis of sample sizes. Using different sample sizes as control variables for subgroup analysis, the results showed that >30 [Z = 3.65, P = .0003], >50 [Z = 2.43, P = .02], >100 [Z = 2.66, P = .008], were significant. After combining the effect values [SMD = −0.49, 95%CI (−0.67, −0.31), P = .03, I2 = 86%], indicating that the sample sizes is one of the factors of heterogeneity in this study.
