INTERNAL PILOT-STUDIES FOR ESTIMATING SAMPLE-SIZE

We develop the idea of using data from the first 'few' patients entere d in a clinical trial to estimate the final trial size needed to have specified power for rejecting H-0 in favour of H-1 if a real differenc e exists. When comparing means derived from Normally distributed data, there is no important effect on test size, power or expected trial si ze, provided that a minimum of about 20 degrees of freedom are used to estimate residual variance. Relative advantages and disadvantages of using larger internal pilot studies are presented. These revolve aroun d crude expectations of the final study size, recruitment rate, durati on of follow-up and practical constraints on the ability to prevent th e circulation of unblinded randomization codes to investigators and th ose involved in editing and checking data.