title: Bias reduction in repeated-measures observational studies by the use of propensity score: the case of enteral sedation for critically ill patients.
abstract: OBJECTIVE
  Within the evidence-based medicine paradigm, randomized controlled trials represent the "gold standard" to produce reliable evidence. Indeed, planning and implementing randomized controlled trials in critical care medicine presents limitations because of intrinsic and structural problems. As a consequence, observational studies still occur frequently. In these cases, propensity score (PS) (probability of receiving a treatment conditional on observed covariates) is an increasingly used technique to adjust the results. Few studies addressed the specific issue of a PS correction of repeated-measures designs.
  
  
  METHODS
  Three techniques for correcting the analysis of nonrandomized designs (matching, stratification, regression adjustment) are presented in a tutorial form and applied to a real case study: the comparison between intravenous and enteral sedative therapy in the intensive care unit setting.
  
  
  RESULTS
  After showing the results before and after the use of PS, we suggest that such a tool allows to partially overcoming the bias associated with the observational nature of the study. It permits to correct the estimates for any observed covariate, while unobserved confounders cannot be controlled for.
  
  
  CONCLUSIONS
  Propensity score represents a useful additional tool to estimate the effects of treatments in nonrandomized studies. In the case study, an enteral sedation approach was equally effective to an intravenous regime, allowing for a lower level of sedation and spare of resources.
authors.affiliation: Dipartimento di Anestesiologia, Terapia Intensiva e Scienze Dermatologiche, Università degli Studi di Milano, Milan, Italy. michele.umbrello@unimi.it
authors.forename: Michele
authors.initials: M
authors.lastname: Umbrello
authors.forename: Giovanni
authors.initials: G
authors.lastname: Mistraletti
authors.forename: Davide
authors.initials: D
authors.lastname: Corbella
authors.forename: Marco
authors.initials: M
authors.lastname: Cigada
authors.forename: Silvia
authors.initials: S
authors.lastname: Salini
authors.forename: Alberto
authors.initials: A
authors.lastname: Morabito
authors.forename: Gaetano
authors.initials: G
authors.lastname: Iapichino
mesh_terms: D000367:Age Factors; D000368:Aged; D002985:Clinical Protocols; D015986:Confounding Factors, Epidemiologic; D016638:Critical Illness; D004333:Drug Administration Routes; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000008:administration & dosage; D007362:Intensive Care Units; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D057216:Propensity Score; D012107:Research Design; D012720:Severity of Illness Index; D012737:Sex Factors
chemical_list: D006993:Hypnotics and Sedatives