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Activity Number: 37
Type: Contributed
Date/Time: Sunday, July 29, 2012 : 2:00 PM to 3:50 PM
Sponsor: Biopharmaceutical Section
Abstract - #306152
Title: Estimation of Controlled Direct Effects for Dynamic Treatment Regimes
Author(s): Tomohiro Shinozaki*+ and Yutaka Matsuyama and Satoshi Iimuro and Yasuo Ohashi and Hideki Ito
Companies: University of Tokyo and University of Tokyo and University of Tokyo and University of Tokyo and Tokyo Metropolitan Geriatric Hospital
Address: 7-3-1 Hongo, Tokyo 113-0033, , Japan
Keywords: causal inference ; g-formula ; treatment regime ; direct effect ; mediation

Comparison of marginal survival probabilities under different dynamic treatment regimes (DTR) would offer clinically relevant decision rules based on patient's covariate history. Despite its pragmatic usefulness, it has rarely been discussed how to assess the mechanisms which the effect of DTR is attributable to, eg, in mediation framework whether the DTR's effect on survival actually relayed through the subsequent covariate targeted in the DTR. In this talk, we propose a method to estimate the controlled direct effects of DTR 'start treatment once after covariate X reaches the value x', where X after treatment is regarded as an intermediate. Using g-computation with parametric modeling, we can effectively simulate complex treatment rules of DTR while adequately controlling an intermediate. The method is applied to data from Japanese Elderly Diabetes Intervention Trial (J-EDIT), a clinical trial of intensive vs. standard diabetic care based on risk factors including serum lipid. Our analyses showed that an effect on cardiovascular risk of the DTR 'start atorvastatin when LDL cholesterol arises above x mg/dL' can be attributed to intensive control of LDL cholesterol thereafter.

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