Sample size Assuming a 20:1:1 sample size ratio between AT% subgroups (AT%> 80%; AT%=70-80%; and AT%<70%, respectively), to detect an increase in the incidence of recurrent events from 0.3 in the control population (AT% > 80%) to 0.6 in each of the other two subgroups (AT%=70-80% and AT%<70%), a sample size of about 900 subjects is needed (power= 95%; α=0.025, to allow for two independent comparisons).