Table 2.

Meta-regression analyses of potential factors.

Factors	N	Std.Err.	t	p	95% CI
Average age of cases	21	0.04	-0.79	0.43	-0.12, 0.05
Average age of controls	21	0.04	-0.72	0.47	-0.11,0.05
Percentage of boys in cases	17	0.01	-0.90	0.37	-0.03,0.01
Percentage of boys in controls	17	0.01	0.90	0.38	-0.01,0.02
Zn/Cu ratio in cases	13	0.06	-1.47	0.14	-0.23, 0.03
Zn/Cu ratio in controls	13	0.09	-1.17	0.24	-0.30, 0.07

N number of included studies; Std.Err standard error; t t statistic, the coefficient divided by its standard error; p an independent variable would be significant (<0.05) or not significant (≥0.05) in the model; CI confidence interval