Purpose: Traditional randomized controlled trials are widely accepted as the gold standard for estimating causal treatment effects. However, they have a significant limitation as strong preferences (or against) one treatment may influence outcomes and/or willingness to participate. To address this limitation, a doubly randomized preference trial (DRPT) has been proposed. We derived the incremental cost-effectiveness ratios (ICERs) for the treatment-preference effects for DRPTs.
Methods: In DRPT, participants are randomly assigned into a “choice” or “no-choice” arm. Participants can choose their preferred treatment (treatment A or B) in the “choice” arm; while in the “no-choice” arm, participants are again randomized into either treatment A or B. With data from a DRPT, the effects of treatment choices on outcomes can be estimated.
Results: ICER for the overall treatment-effect can be estimated (given treatment choice vs. given no-choice of treatment): ICEROverall_TPE = {(TPEA + TPEB)cost} / {(TPEA + TPEB)QALY}. ICER for the treatment-preference of treatment A (TPEA): ICERTPE_A = {(TPEA)cost} / {(TPEA)QALY}. ICER for the treatment-preference of treatment A (TPEB): ICERTPE_B = {(TPEB)cost} / {(TPEB)QALY}. Where, TPEA = {Π(1 - p)µA(A) - (1 - Π)pµB(A)} and TPEB = {(1 - Π)pµB(B) - Π(1 - p)µA(B)}. µA(A) and µB(B) are the estimated mean outcomes corresponding to patients who received their preferred treatment A and B in the choice arm, respectively. µB(A) and µA(B) are the estimated mean outcome corresponding to patients who receive treatment A and B but actually prefer treatment B and A, respectively. And µ can be the estimated mean cost or QALY outcome. Π is the estimated proportion of the population who prefer treatment A and (1 – Π) is the estimated proportion of the population who prefer treatment B. And p is the proportion of patients who are randomly assigned to treatment A, and (1 – p) is the proportion of those randomized to treatment B. Using data from a DRPT examining the treatment effect and treatment-preference effects between cognitive behavioral therapy (CBT) and pharmacotherapy with sertraline (SER), we estimated the ICERs for the overall treatment-preference effect, treatment-preference of CBT, and treatment preference of SER to be dominant, $22,494/QALY (less cost and less QALY), and $15,647/QALY, respectively.
Conclusion: ICER estimates for the effects of treatment choices in DRPT are established and can be used in cost-effectiveness studies.
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