Table 3.

Meta-regression analysis to determine sources of heterogeneity for all 11 studies and subgroup of all prospective studies

Covariate	coefficient	p-value	RDOR	95% CI
Meta-analysis
Sex (ratio of male vs. female)	−1.23	0.81	0.29	(0.0, >1000)
Sample size	0.09	0.31	1.09	(0.89, 1.33)
Design (prospective vs. retrospective)	0.24	0.94	1.27	(0.0, >1000)
Center (multi-center vs. single center)	−8.72	0.26	0	(0.0, >1000)
Country (America vs. non-America)	−1.73	0.75	0.18	(0.0, >1000)
Needle size*	−0.95	0.49	0.39	(0.02, 8.48)
Subgroup (Prospective Studies) Analysis
Sex (ratio of male vs. female)	22.3	0.2	>1000	(0,>1000)
Sample size	−0.06	0.18	0.94	(0.75, 1.17)
Center (multi-center vs. single center)	−3.91	0.17	0.02	(0,>1000)
Country (America vs. non-America)	−5.61	0.48	0	(0,>1000)
Needle size	1.65	0.55	5.19	(0, >1000)

^*based on uni-variate meta-regression and reduced data (centers = 10)