Table 5. Effects of study variables by meta-regression.

Covariant	Coefficient	P value	95% CIs
Country(Ref = Europe)
Asia	−0.004	0.991	−0.740 to 0.732
United States	−0.161	0.475	−0.640 to 0.318
Adujusted for covariates	−0.243	0.180	−0.615 to 0.129
Sample size	−0.633	0.115	−1.445 to 0.179
Newcastle—Ottawa Scale scores	−0.051	0.451	−0.193 to 0.091
year of publication	-0.014	0.276	−0.039 to 0.012