Improving the Estimation of Site-Specific Effects and their Distribution in Multisite Trials
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In multisite trials, statistical goals often include obtaining individual site-specific treatment effects, determining their rankings, and examining their distribution across multiple sites. This paper explores two strategies for improving inferences related to site-specific effects: (a) semiparametric modeling of the prior distribution using Dirichlet process mixture (DPM) models to relax the normality assumption, and (b) using estimators other than the posterior mean, such as the constrained Bayes or triple-goal estimators, to summarize the posterior. We conduct a large-scale simulation study, calibrated to multisite trials common in education research. We then explore the conditions and degrees to which these strategies and their combinations succeed or falter in the limited data environments. We found that the average reliability of within-site effect estimates is crucial for determining effective estimation strategies. In settings with low-to-moderate data informativeness, flexible DPM models perform no better than the simple parametric Gaussian model coupled with a posterior summary method tailored to a specific inferential goal. DPM models outperform Gaussian models only in select high-information settings, indicating considerable sensitivity to the level of cross-site information available in the data. We discuss the implications of our findings for balancing trade-offs associated with shrinkage for the design and analysis of future multisite randomized experiments.
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