Table 4. The meta-regression results among 8 studies.

	Coefficient	Standard error	T value	P value	95% Confidence interval
RR	0.8320814	0.114808	7.25	0.019*	0.3381026∼1.32606
Control size	0.0273875	0.0028546	9.59	0.011*	0.015105∼0.03967
Region	−1.174875	0.1413874	−8.31	0.014*	−1.783216∼−0.5665344
Publication year	0.1874112	0.0250733	7.47	0.017*	0.0795295∼0.2952929
Total size	−0.0120356	0.0012977	−9.27	0.011*	−0.0176192∼-0.0064519
Cons	−374.732	50.28602	−7.45	0.018*	−591.0953∼−158.3687

Abbreviations: Control size: Control group sample size; Total size: Total sample size; RR: the ratio of case size to control size; Coefficient: regression coefficient;The regression coefficients are the estimated increase in the lnOR per unit increase in the covariate as control size, RR, total size, region and publication year; cons:constant item.

^*P<0.05.