RESEARCH COST ANALYSES TO AID IN DECISION-MAKING IN THE CONDUCT OF A LARGE PREVENTION TRIAL, CARET

Because of their larger study populations and longer durations, preven tion trials typically are more costly than treatment trials. Thus it i s important to analyze costs systematically to aid in making cost-effe ctive decisions during the conduct of prevention trials as well as in the original design. Cost analysis must be tied to sample size estimat ion because costs depend on such factors as the total number of person -years of follow-up and the number of trial outcomes, which are not ba sic design parameters but are derived quantities resulting from sample size estimation. We illustrate the use of cost analysis to decide amo ng options for future conduct of an ongoing prevention trial with thre e issues that have arisen during the Carotene and Retinol Efficacy Tri al (CARET): the trade-off between extending the duration of the trial or increasing the number of participants, the effect on costs of delay in accrual, and the cost effectiveness of particular retention activi ties.