Revista Española de Cardiología (English Edition) Revista Española de Cardiología (English Edition)
Rev Esp Cardiol. 2005;58:126-36 - Vol. 58 Num.02 DOI: 10.1016/S1885-5857(06)60355-1

Analysis With the Propensity Score of the Association Between Likelihood of Treatment and Event of Interest in Observational Studies. An Example With Myocardial Reperfusion

Helena Martí a, Jon Pérez-Bárcena b, Miquel Fiol b, Jaume Marrugat c, Carmen Navarro d, Elena Aldasoro e, Adolfo Cabadés f, Antonio Segura g, Rafael Masiá h, Javier Turumbay i, Lluís Cirera d, José M Arteagoitia e, Carlos A Tomás j, Gema Vega k, Joan Sala h, Enrique de los Arcos l, María J Tormo d, Iraida Hurtado-de-Saracho e, Mercedes Francés-Sempere m, Roberto Elosua a

a Unidad de Lípidos y Epidemiología Cardiovascular, IMIM. Barcelona, Spain.
b Institut Universitari de Ciències de la Salut (IUNICS), Palma de Mallorca, Spain.
c Unidad de Lípidos y Epidemiología Cardiovascular, IMIM. Barcelona, Spain. Universidad Autónoma de Barcelona, Barcelona, Spain.
d Departamento de Epidemiología, Consejería de Sanidad y Consumo, Murcia, Spain.
e Departamento de Sanidad, Gobierno Vasco, Vitoria-Gasteiz, Spain.
f Unidad de Cuidados Intensivos, Hospital La Fe, Valencia, Spain.
g Instituto de Ciencias de la Salud, Consejería de Sanidad de Castilla-La Mancha, Talavera de la Reina, Toledo, Spain.
h Servicio de Cardiología, Hospital Josep Trueta, Girona, Spain.
i Hospital Reina Sofía de Tudela, Navarra, Spain.
j Hospital de la Ribera, Alcira, Valencia, Spain.
k Unidad de Cuidados Intensivos, Complejo Hospitalario de Albacete, Albacete, Spain.
l Hospital de Navarra, Pamplona, Navarra, Spain.
m Hospital Arnau de Vilanova, Valencia, Spain.

Keywords

Myocardial infarction. Prognosis. Reperfusion. Thrombolysis.

Abstract

Introduction and objectives. Analysis of the effect of treatment in observational studies is complex due to differences between treated and nontreated patients. Calculating the probability of receiving treatment conditioned on relevant covariates (propensity score [PS]) has been proposed as a method to control for these differences. We report an application of PS to assess the association between reperfusion treatment and 28-day case fatality in patients with acute myocardial infarction (AMI). Method. We describe the procedure used to calculate PS for receiving reperfusion treatment, and different strategies to analyze the association between PS and case fatality with regression modeling and matching. Data were from a population-based registry of 6307 patients with AMI in Spain during 1997-98. Results. The PS for reperfusion was calculated in 5622 patients. In the multivariate analysis, reperfusion was associated with lower case fatality (OR = 0.59; 95% confidence interval [95% CI]: 0.46-0.77). When PS was included as a covariate, this association became non- significant (OR = 0.76; 95% CI: 0.57-1.01). In the subgroup of matched patients with a similar PS (n = 3138), treatment was not associated with case fatality (OR = 0.95; 95% CI: 0.72-1.26). When the influence of cases with missing data on PS was controlled for, reperfusion treatment was associated with lower fatality (OR = 0.66; 95% CI: 0.55-0.80). Conclusions. Calculating propensity score is a method that controls for differences between treated and nontreated patients. This score has limitations when matching is incomplete and when data are missing. Results of the present example suggest that reperfusion treatment reduces AMI case fatality.

1885-5857/© 2005 Sociedad Española de Cardiología. Published by Elsevier España, S.L.U. All rights reserved

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