I need your help to compute a power analysis for survival analysis (Kaplan meier) without historical data. In my lab we are preparing a project in which we want to evaluate tumor free survival of two cohorts of mouse (one treated with A and one treated with B); because the experiment is new, we don't know the median tumor incidence time of the two groups.
We want to make sure to detect at least a difference in tumor incidence of 20% between the two groups (using less mouse as possible). I fixed alpha=0.05 and power=0.8. How can I calculate the required sample size (using R or STATA)? How can I calculate the hazard ratio??
Thank you in advance for your help! .. and sorry for my english errors