An Analysis of Incentive Schemes for Participant Retention in Clinical Studies

Abstract

Participant retention is one of the significant issues faced by clinical studies. Various factors, such as expected health benefits, logistics expenses, and inconvenience during the study, impact retention rate. In this paper, we focus on analyzing mechanisms that combine both monetary payments and the effort of a clinic to improve retention. In particular, we consider a clinic that conducts a clinical study and a set of participants characterized by their health conditions, logistics expenses, and inconvenience costs. The clinic offers monetary payments to participants and exerts effort to reduce inconvenience. The participants decide to complete or leave the study based on their utilities. Considering the participants' decisions, the clinic minimizes his cost of achieving a desirable retention rate. Given a participant-specific linear payment scheme, we model the clinic's problem as a non-linear 0--1 integer program and propose a polynomial-time algorithm to solve it under full information. We further modify this algorithm to solve the clinic's problem under two commonly observed incentive schemes--- the Fixed Payment scheme and the Logistics Reimbursement scheme. Then, we conduct a comprehensive computational study to gain insights on how participant population, clinic, and study characteristics affect the relative performance of these schemes. Our analysis highlights that by optimally designing a participant-specific scheme, the clinic can reduce his cost by about 47\% on average compared to that under the reimbursement and fixed payment schemes. We also extend our analysis to a setting where the clinic does not observe participants' characteristics and show that the performance of the reimbursement scheme is robust to this information asymmetry. Further, if the clinic prefers a fixed payment scheme, it benefits significantly from acquiring information on participants' characteristics.