title: Performing both propensity score and instrumental variable analyses in observational studies often leads to discrepant results: a systematic review.
abstract: OBJECTIVE
  Propensity score (PS) and instrumental variable (IV) are analytical techniques used to adjust for confounding in observational research. More and more, they seem to be used simultaneously in studies evaluating health interventions. The present review aimed to analyze the agreement between PS and IV results in medical research published to date.
  
  
  METHODS
  Review of all published observational studies that evaluated a clinical intervention using simultaneously PS and IV analyses, as identified in MEDLINE and Web of Science.
  
  
  RESULTS
  Thirty-seven studies, most of them published during the previous 5 years, reported 55 comparisons between results from PS and IV analyses. There was a slight/fair agreement between the methods [Cohen's kappa coefficient = 0.21 (95% confidence interval: 0.00, 0.41)]. In 23 cases (42%), results were nonsignificant for one method and significant for the other, and IV analysis results were nonsignificant in most situations (87%).
  
  
  CONCLUSIONS
  Discrepancies are frequent between PS and IV analyses and can be interpreted in various ways. This suggests that researchers should carefully consider their analytical choices, and readers should be cautious when interpreting results, until further studies clarify the respective roles of the two methods in observational comparative effectiveness research.
authors.affiliation: Lorraine University, Paris-Descartes University, EA 4360 Apemac, Avenue de la forêt de Haye, 54500 Vandoeuvre-lès-Nancy, France; Université Paris 13, Sorbonne Paris Cité, UFR SMBH, 1 rue de Chablis, 93017, Bobigny, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Laborde-Castérot
authors.affiliation: Lorraine University, Paris-Descartes University, EA 4360 Apemac, Avenue de la forêt de Haye, 54500 Vandoeuvre-lès-Nancy, France; Clinical Epidemiology and Evaluation, CIC-EC CIE6 Inserm, University Hospital of Nancy, Allée du Morvan, 54500 Vandoeuvre-lès-Nancy, France.
authors.forename: Nelly
authors.initials: N
authors.lastname: Agrinier
authors.affiliation: Lorraine University, Paris-Descartes University, EA 4360 Apemac, Avenue de la forêt de Haye, 54500 Vandoeuvre-lès-Nancy, France; Clinical Epidemiology and Evaluation, CIC-EC CIE6 Inserm, University Hospital of Nancy, Allée du Morvan, 54500 Vandoeuvre-lès-Nancy, France. Electronic address: n.thilly@chu-nancy.fr.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Thilly
mesh_terms: D057186:Comparative Effectiveness Research / Q000379:methods*; D006801:Humans; D015233:Models, Statistical; D064887:Observational Studies as Topic / Q000379:methods / Q000592:standards*; D057216:Propensity Score; D015203:Reproducibility of Results
keywords: Comparative effectiveness research; Confounding by indication; Instrumental variable; Observational studies; Propensity score; Statistical methods