Table 1.

A summary of selection bias prior to matching and bias reduction post matching

Matching Method	Sample Size	SB for Logit of PS (%)	PBR for Logit of PS (%)	Average of Absolute SB across 74 Covariates (%)	Average of PBR across 74 Covariates (%)
Prior to Matching	n R = 1990 n U = 4327	78.73	—	16.22	—
Post Matching
Nearest Neighbor	n R = n U = 1990	30.23	75.21	4.84	53.32
Optimal	n R = n U = 1990	30.23	75.21	4.91	55.15
Mahalanobis Caliper	n R = n U = 1701	61.04	51.79	10.16	25.70
Caliper	n R = n U = 1539	1.96	98.41	1.00	76.78
50 % Interval	n R = n U = 1483	−2.89	97.69	1.43	76.50
68 % Interval	n R = n U = 1538	−0.46	99.64	1.25	79.24
95 % Interval	n R = n U = 1713	9.52	92.55	1.33	79.12