Propensity scores in intensive care and anaesthesiology literature: a systematic review

Propensity score methods have been increasingly used in the last 10 years. However, the practical use of the propensity score (PS) has been reported as heterogeneous in several papers reviewing the use of propensity scores and giving some advice. No precedent work has focused on the specific application of PS in intensive care and anaesthesiology literature. After a brief development of the theory of propensity score, to assess the use and the quality of reporting of PS studies in intensive care and anaesthesiology, and to evaluate how past reviews have influenced the quality of the reporting. Forty-seven articles published between 2006 and 2009 in the intensive care and anaesthesiology literature were evaluated. We extracted the characteristics of the report, the type of analysis, the details of matching procedures, the number of patients in treated and control groups, and the number of covariates included in the PS models. Of the 47 articles reviewed, 26 used matching on PS, 12 used stratification on PS and 9 used adjustment on PS. The method used was reported in 81% of the articles, and the choice to conduct a paired analysis or not was reported in only 15%. The comparison with the previously published reviews showed little improvement in reporting in the last few years. The quality of reporting propensity scores in intensive care and anaesthesiology literature should be improved. We provide some recommendations to the investigators in order to improve the reporting of PS analyses.