TABLE 4.

Meta-regression for overall effects.

Random effects	Coefficient	Standard error	95% lower	95% upper	Z-value	P-value
Intercept	0.181***	0.042	0.100	0.262	4.36	0.000
Design (RCT)	−0.088*	0.038	–0.162	–0.014	–2.33	0.020
Sample size (Small)	0.077*	0.038	0.003	0.151	2.04	0.041
Grade (Pre-kindergarten)	0.082	0.066	–0.048	0.211	1.23	0.218
Duration (more than one year)	0.010	0.037	–0.063	0.083	0.27	0.788
Dosage (low)	−0.122***	0.033	–0.187	–0.057	–3.68	0.000
Dosage (NA)	–0.045	0.061	–0.165	0.075	–0.73	0.465

In meta-regression, the number of studies was 20, and the number of effect size was 177.

*p < 0.05, **p < 0.01, ***p < 0.001.