Large Sample Inference with Dynamic Information Borrowing

Large sample behavior of dynamic information borrowing (DIB) estimators is investigated. Asymptotic properties of several DIB approaches (adaptive risk minimization, adaptive LASSO, Bayesian procedures with empirical power prior, fully Bayesian procedures, and a Bayes-frequentist compromise) are explored against shrinking to zero alternatives. As shown theoretically and with simulations, local asymptotic distributions of DIB estimators are often non-normal. A simple Gaussian setting with external information borrowing illustrates that none of the considered DIB methods outperforms others in terms of mean squared error (MSE): at different conflict values, the MSEs of DIBs are changing between the MSEs of the maximum likelihood estimators based on the current and pooled data. To uniquely determine an optimality criterion for DIB, a prior distribution on the conflict needs be either implicitly or explicitly determined using data independent considerations. Data independent assumptions on the conflict are also needed for DIB-based hypothesis testing. New families of DIB estimators parameterized by a sensitivity-to-conflict parameter S are suggested and their use is illustrated in an infant mortality example. The choice of S is determined in a data-independent manner by a cost-benefit compromise associated with the use of external data.