The program uses the method of Peterson, B. and George, S.L. (1993). Controlled Clinical Trials, 511-522 but where the expected probability of event for each stratum is calculated using the accrual, follow-up and exponential failure and competing risk assumptions. The total sample size is calculated as follows
N=(q(1-a/2)+q(1-b))2 * S[1/(eij*lij)]/D2
Where fij are the cell frequencies and eij are the event probabilities in treatment i and stratum j, q is the inverse normal function, andD=log(D1/D2)
Dj=l1j/l2j is the hazard ratio for the treatment effect within stratum j
The user is prompted for values to the following items. For items that have initial default values set, the values are given in parentheses.