I'm trying to work out the sample size needed for an RCT based on a small study looking at reoperation following index surgery. In this small study, there were 1000 patients, group 1 had 700 versus group 2 had 300 patients. In group 1 there were 20 reoperations and in group 2 there were 30 reoperations. However, survival at 10 years was 15% in group 1 and 12% in group 2. So most patients were no longer at risk of a reoperation. I'm wondering how I would work out the sample size needed for an RCT randomising 1:1 and looking at find a difference of 0.10 reduction in hazard ratio between groups if following up patients for 10 years accounting for death during the follow up period please? My stata code currently looks like this
power cox, hratio(0.90) alpha(0.05) power(0.80)
power cox, hratio(0.90) alpha(0.05) power(0.80)
