Li, Gang et al., A sample size adjustment procedure for clinical trials based on conditional power, Biostatistics (Oxford. Print) , 3(2), 2002, pp. 277-287
When designing clinical trials, researchers often encounter the uncertainty in the treatment effect or variability assumptions.Hence the sample size calculation at the planning stage of a clinical trial may also be questionable.Adjustment of the sample size during the mid.course of a clinical trial has become a popular strategy lately.In this paper we propose a procedure for calculating additional sample size needed based on conditional power, and adjusting the final.stage critical value to protect the overall type I error rate.Compared to other previous procedures, the proposed procedure uses the definition of the conditional type I error directly without appealing to an extra special function for it.It has better flexibility in setting up interim decision rules and the final.stage test is a likelihood ratio test.