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. Author manuscript; available in PMC: 2017 Mar 1.
Published in final edited form as: Contemp Clin Trials. 2015 Dec 17;47:85–92. doi: 10.1016/j.cct.2015.12.012

Figure 1.

Figure 1

Histograms and density curves of the logit of propensity scores for 500 smokers and 500 nonsmokers. The same smokers were used in both (a) and (b), while the nonsmokers were selected randomly in (a) and by distance in (b).