Contrasting Evidence Within and Between Institutions That Supply Treatment in an Observational Study of Alternative Forms of Anesthesia

• Activity Number: 113
• Type: Topic Contributed
• Date/Time: Monday, August 1, 2011 : 8:30 AM to 10:20 AM
• Sponsor: Section on Health Policy Statistics
• Author(s): Jose R. Zubizarreta*+ and Mark Neuman and Jeffrey H. Silber and Paul R. Rosenbaum
• Companies: University of Pennsylvania and University of Pennsylvania and The Children's Hospital of Philadelphia and University of Pennsylvania
• Keywords: Evidence factor ; Fine balance ; Optimal subset matching ; Sensitivity analysis

Abstract

A new matched design is proposed for contrasting evidence within and between institutions that supply treatment in an observational study. Using a new extension of optimal matching with fine balance, a first type of pairs exactly balance treatment assignment across institutions, so differences between institutions that affect everyone in the same way cannot bias this comparison. A second type of pairs compare institutions that assign most subjects to treatment and other institutions that assign most subjects to control, so each institution is represented in the treated group if it typically assigns subjects to treatment or alternatively in the control group if it typically assigns subjects to control. The design provides two evidence factors, that is, two tests of the null hypothesis of no treatment effect that are independent when the null hypothesis is true, where each factor is largely unaffected by certain unmeasured biases that could readily invalidate the other factor. The two factors permit separate and combined sensitivity analyses, where the magnitude of bias affecting the two factors may differ. The case of knee surgery with forms of anesthesia is considered in detail.