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. Author manuscript; available in PMC: 2015 Dec 8.
Published in final edited form as: J Am Stat Assoc. 2012;107(499):901–915. doi: 10.1080/01621459.2012.682533

Figure 2.

Figure 2

Balance on 44 covariates compared to balance expected from complete randomization. The figure contains three quantile quantile plots of 44 P values against the uniform distribution. The P-values contrast the marginal distributions of the 44 covariates in the regional and general anesthesia groups, for 2708 patients in type 1 matches, 1888 patients in type 2 matches and 4596 = 2708 + 1888 patients in both types combined. For continuous covariates, the P values are from Wilcoxon’s rank sum test, and for binary covariates they are from Fisher’s exact test for a 2×2 table. All 132 = 3 × 44 P-values are greater than 0.05, and they are larger than expected from a uniform distribution.