Table 1

Contingency table between choice of prior for Bayesian constant accrual model9 10 and investigator beliefs  (sceptical vs optimistic) and/or trial features (small vs large sample size at interim reviews of accrual performance)

Prior choice
Inverse gamma prior depending on constant PAccelerated priorHedging prior
Sceptical prior built around the position that the planned enrolment target is unlikely to be achieved in the given time‘small’ P
(ie, if P=0.25 the prior is given weight equivalent to one-fourth the proposed sample size)
Performs much like the sceptical prior when the accrual is extremely off target
Optimistic prior built around the position that the planned enrolment target is likely to be achieved in the given time‘large’ P
(ie, if P=1 the prior is given weight equivalent to the proposed sample size)
Performs similar to an optimistic priorPerforms much like the optimistic prior when the accrual is on target or only slightly off target
Small sample size at interimUse different priors and conduct sensitivity analyses to assess the influence of the prior specification on the conclusions
Large sample size at interimDesigned to transition rapidly from an optimistic to a sceptical prior when more accrual data are available