Comparing Methods of Expert Elicitation for Treatment Effect or Borrowing Parameters in Standard and Rare Disease Clinical Trials: A Systematic Mapping Study

Abstract: Expert elicitation is an invaluable tool for gaining insights into the degree of clinical knowledge surrounding parameters of interest when designing, or supplementing trial data when analysing, a clinical trial. Elicitation is considered particularly useful in cases where limited data are available, such as in rare diseases. This study aims to identify methods of expert elicitation and aggregation for treatment effect or borrowing parameters that are used in the design or analysis stages of clinical trials. A comprehensive review of statistical and non-statistical literature was conducted by database searching, and reference list screening of older, relevant literature reviews. The search took place in October 2024 and identified 366 potentially relevant publications. Of these, 126 were selected for full-text review based on review of titles and abstracts, and 41 publications were deemed eligible for inclusion after a full reading. For each included publication, data were extracted on methods of elicitation and aggregation, the types of parameters elicited, the resulting distributions, the number of experts used, and any training provided to experts. Publication characteristics such as contribution type, journal type, and application to the rare disease setting was also noted. A narrative description of the selected publications was produced, detailing 6 unique methods for expert elicitation and 10 unique methods for aggregation. We discuss the most popular methods used across standard and rare disease clinical trials, along with any strengths and limitations. Overall, there is no formal framework for expert elicitation in clinical trials, and more general methods are applied with little consideration into the specific context and trial designs. This review identifies the methodological gaps in current practice, providing a foundation for future development.