*2.4. Synthesis Methods*

In this study, differences in FMS proficiency among boys and girls were compared using Review Manager version 5.4.1 from the Cochrane Assistance Network. The data in this paper are continuous variables, and the comprehensive effect index is the Standard Mean Difference (SMD) and its 95% CI. SMD was interpreted as very small (<0.2), small (0.2–0.5), moderate (0.5–0.8) and large (>0.8) [25], where *p* < 0.05 indicates significant differences between the genders. The I-squared (I<sup>2</sup> ) statistic was used to test the heterogeneity between studies. When I<sup>2</sup> <sup>≤</sup> 50, there was no heterogeneity between studies, and a fixedeffects model was used for meta-analysis; when I<sup>2</sup> > 50, there was heterogeneity between studies, and a random-effects model was used for meta-analysis [26]. The pooled results showed heterogeneity between studies, which we addressed by meta-regression analysis and subgroup analysis. In addition, we sequentially excluded literature for sensitivity analysis, evaluated the stability of the combined results of the meta-analysis and verified the existence of publication bias in the included studies using Egger's test.

When more than two subgroups needed to be merged in the research, the first two subgroups were merged first, then the third subgroup was merged, and so on. The merge formula is as follows [27]:

$$SD = \sqrt{\frac{(N\_1 - 1)SD\_1^2 + (N\_2 - 1)SD\_2^2 + \frac{N\_1N\_2}{(N\_1 + N\_2)}\left(M\_1^2 + M\_2^2 - 2M\_1M\_2\right)}{N\_1 + N\_2 - 1}}$$

where *SD* is standard deviation; Group 1 sample size is *N*1, mean is *M*1, standard deviation is *SD*1; and Group 2 sample size is *N*2, mean is *M*2, and standard deviation is *SD*2.
