On the estimation of the median odds ratio for measuring contextual effects in multilevel binary data from complex survey designs
In studies with clustered or hierarchical data structures, quantifying between-cluster heterogeneity, referred to as contextual effects, is crucial for valid cluster-level inference. The median odds ratio (MOR), derived from random effects (RE) logistic regression models for clustered binary data, provides an intuitive assessment of contextual effects. Most existing research focuses on point estimation of the MOR for two-level models, with limited exploration of its statistical properties under complex multilevel structures. However, the development of corresponding interval estimators is essential for statistical inference. Moreover, many real-world datasets, particularly those from multistage surveys, involve hierarchical structures beyond two levels, where contextual effects at each level are of interest. This paper discusses the estimation of MOR for both the two-and three-level binary data, with particular emphasis on interval estimation. Since the MOR is a post-estimation measure based on variance components of the RE logit model, its confidence interval is derived using the Delta method, treating the log-transformed MOR as asymptotically normal. The approach is demonstrated across different model specifications in two-and three-level settings. An extensive simulation study evaluated the performance of the MOR estimators across diverse scenarios in hierarchical data settings. The results showed that the estimators exhibited negligible bias and satisfactory coverage probability of a 95% confidence interval for moderate to large samples, with small-sample bias mainly due to variance component estimation. An application of the methods for estimating the contextual effect on C-section delivery demonstrated that the proposed framework enhances interpretability and supports more informed statistical and policy-oriented analyses.