Using Simulation When Only Minimal Information Is Available to Estimate the Design Effect for an Ebola Vaccine Evaluation Study

• Activity Number: 192
• Type: Contributed
• Date/Time: Monday, August 10, 2015 : 10:30 AM to 12:20 PM
• Sponsor: Biopharmaceutical Section
• Author(s): Charles Rose* and Paul Gargiullo and Benjamin Lopman and Manoj Gambhir
• Companies: CDC and CDC and CDC and CDC
• Keywords: Randomized Trial ; Group Randomized Trial ; Design Effect ; Vaccine Efficacy ; Ebola ; Simulation

Abstract

Randomized trials (RT) are the benchmark for estimating vaccine efficacy (VE). When individuals cannot be practically randomized to a study arm, a group RT (GRT) may be an attractive alternative despite a loss of statistical efficiency, i.e., an inflated standard error, for estimating VE. This loss of efficiency is often referred to as the design effect (DEFF) or variance inflation factor (VIF). Failure to account for the lack of independence among individuals within a group during the design stage may result in an underpowered GRT with an inadequate sample size. An estimate of the intraclass correlation (ICC) is usually necessary to estimate the DEFF. Estimates of the DEFF or ICC are often challenging to obtain, especially for a novel vaccine or drug. In the study design phase for an evaluation to estimate the efficacy of a candidate Ebola vaccine there is an absence of information on the DEFF or ICC. We use a minimal amount of field data available from Sierra Leone on the Ebola incidence and RT groups (types and sizes) to conduct a simulation to estimate ICC and DEFF.