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A mixed model approach to estimate the survivor average causal effect in cluster-randomized trials

Wang, W., Tong, G., Hirani, S. P. ORCID: 0000-0002-1577-8806 , Newman, S. P. ORCID: 0000-0001-6712-6079, Halpern, S. D., Small, D. S., Li, F. & Harhay, M. O. (2023). A mixed model approach to estimate the survivor average causal effect in cluster-randomized trials. Staistics in Medicine, 43(1), pp. 16-33. doi: 10.1002/sim.9939


In many medical studies, the outcome measure (such as quality of life, QOL) for some study participants becomes informatively truncated (censored, missing, or unobserved) due to death or other forms of dropout, creating a nonignorable missing data problem. In such cases, the use of a composite outcome or imputation methods that fill in unmeasurable QOL values for those who died rely on strong and untestable assumptions and may be conceptually unappealing to certain stakeholders when estimating a treatment effect. The survivor average causal effect (SACE) is an alternative causal estimand that surmounts some of these issues. While principal stratification has been applied to estimate the SACE in individually randomized trials, methods for estimating the SACE in cluster-randomized trials are currently limited. To address this gap, we develop a mixed model approach along with an expectation–maximization algorithm to estimate the SACE in cluster-randomized trials. We model the continuous outcome measure with a random intercept to account for intracluster correlations due to cluster-level randomization, and model the principal strata membership both with and without a random intercept. In simulations, we compare the performance of our approaches with an existing fixed-effects approach to illustrate the importance of accounting for clustering in cluster-randomized trials. The methodology is then illustrated using a cluster-randomized trial of telecare and assistive technology on health-related QOL in the elderly.

Publication Type: Article
Additional Information: This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. © 2023 The Authors. Statistics in Medicine published by John Wiley & Sons Ltd.
Publisher Keywords: causal inference, cluster-randomized trials, linear mixed models, expectation–maximization, potential outcomes, principal stratification
Subjects: H Social Sciences > HN Social history and conditions. Social problems. Social reform
R Medicine
Departments: School of Health & Psychological Sciences > Healthcare Services Research & Management
SWORD Depositor:
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