  With the continued increase in the use of Bayesian methods in drug
development, there is a need for statisticians to have tools to develop robust
and defensible informative prior distributions. Whilst relevant empirical data
should, where possible, provide the basis for such priors, it is often the case
that limitations in data and/or our understanding may preclude direct
construction of a data-based prior. Formal expert elicitation methods are a key
technique that can be used to determine priors in these situations. Within
GlaxoSmithKline (GSK), we have adopted a structured approach to prior
elicitation based on the SHELF elicitation framework, and routinely use this in
conjunction with calculation of probability of success (assurance) of the next
study(s) to inform internal decision making at key project milestones. The aim
of this paper is to share our experiences of embedding the use of prior
elicitation within a large pharmaceutical company, highlighting both the
benefits and challenges of prior elicitation through a series of case studies.
We have found that putting team beliefs into the shape of a quantitative
probability distribution provides a firm anchor for all internal decision
making, enabling teams to provide investment boards with formally appropriate
estimates of the probability of trial success as well as robust plans for
interim decision rules where appropriate. As an added benefit, the elicitation
process provides transparency about the beliefs and risks of the potential
medicine, ultimately enabling better portfolio and company-wide decision
making.
