Emerging Analytical Techniques for Comparative Effectiveness Research Steven M. Brunelli, MD, MSCE, Jeremy A. Rassen, ScD  American Journal of Kidney Diseases  Volume 61, Issue 1, Pages 13-17 (January 2013) DOI: 10.1053/j.ajkd.2012.08.030 Copyright © 2012 National Kidney Foundation, Inc. Terms and Conditions

Figure 1 Schematic depiction of propensity score (ps) and inverse probability of treatment weighting (IPTW) analyses. These hypothetical examples consider the association of treatment (tx) A (indicated by tx_a=1) versus a comparator (denoted tx_a=0) with death. (A) Estimation of the ps, which is the probability that the patient received tx A based on 2 covariates: age and race. First, age and race data are used to estimate a regression equation for receipt of tx A, and next, a ps for each patient is calculated by inputting each patient's age and race into the equation. (B) Propensity matching: tx A and comparator patients with similar ps values are paired together for inclusion in outcome models, whereas patients for whom a suitable match cannot be found are excluded from the analysis. This results in balance of ps between tx A and comparator patients. (C) Stratified ps analysis: boundaries are identified that represent the 2.5th percentile of ps in tx A patients and the 97.5th percentile of ps in comparator patients, and all those with a ps outside of this range are excluded. The remaining patients are stratified into deciles of ps. (D) IPTW analysis: the probability of treatment is equal to the ps for tx A patients and, for comparator patients, 1 – ps. IPTW values are applied as the reciprocal of probability of treatment (denoted “pt”), such that patients for whom the exposure status was more random (eg, patient 10) have far greater influence on the models (count as the equivalent of 10 patients), whereas patients for whom treatment status was predictable (eg, patient 6) have less influence (count as the equivalent of only one patient). American Journal of Kidney Diseases 2013 61, 13-17DOI: (10.1053/j.ajkd.2012.08.030) Copyright © 2012 National Kidney Foundation, Inc. Terms and Conditions