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. 2012 Aug 16;12:10. doi: 10.1186/1471-2326-12-10

Figure 1.

Figure 1

Illustration of the different distributions of a covariate (X) in two non-randomized samples (A & B). The propensity score method (PS) aims at re-creating the conditions of a pseudorandomization, while the inverse probability weighting (IPW) approach aims at re-creating a pseudopopulation where patients A and B are exchangeable. Both methods aim at obtaining a similar distribution of the covariate X in the two groups.