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Does higher spending improve survival outcomes for myocardial infarction? Examining the cost-outcomes relationship using time-varying covariates


Objectives — Previous patient-level acute myocardial infarction (AMI) research has found higher hospital spending to be associated with improved survival; however, survivor-treatment selection bias traditionally has been overlooked. The purpose of this study was to examine the AMI cost-outcome relationship, taking into account this form of bias.

Data Sources — Hospital Discharge Abstract data tracked costs for AMI hospitalizations. Ontario Vital Statistics data tracked patient mortality.

Study Design — A standard Cox survival model was compared to an extended Cox model using hospital costs as a time-varying covariate to examine the impact of cost on 1-year survival in a cohort of 30,939 first-time AMI patients in Ontario, Canada, from 2007 to 2010.

Principal Findings — Higher patient-level AMI spending decreased the hazard of dying (Standard Model: log-cost hazard ratio: 0.513, 95 percent CI: 0.479–0.549; Extended Model: log-cost hazard ratio: 0.700, 95 percent CI: 0.645–0.758); however, the protective effect was overestimated by 62 percent when survivor-treatment bias was overlooked. In the extended model, a 10 percent increase in spending was associated with a 3.6 percent decrease in hazard of death.

Conclusion — The findings of this study suggest that if survivor-treatment bias is overlooked, future research may materially overstate the protective effect of patient-level spending on outcomes.



Cohen D, Manuel DG, Tugwell P, Sanmartin C, Ramsay T. Health Serv Res. 2015; 50(5):1589-605. Epub 2015 Feb 9.

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