I am are currently evaluating risk factors associated with a virus A , incidence among patients with a follow-up sample of 312. Overall, the virus incidence rate is estimated at 4.7 per 100 pyr, 95% CI (3.0-7.4), with a total follow-up time of 383.9 person years and 18 incidence cases. How can I do a power calculation based on assumptions of the virus acquisition in patients who have virus B? For a rate that is twice as high, four times as high, and even eight times higher. Virus B Yes- 203 No-109 I have tried using which gives a very suscpicious power? v <- qnorm(0.975) mu <- 0.047 muEst <- 0.094 #for a rate twice as high n <- 312 #top left <- (n*((muEst-mu)^2))/mu left <- sqrt(left) ucalc<-left -v ucalc pnorm(ucalc) The formula used is at Essential Medical Statistics Book by Betty R Kirkwood et al pg 420 formula 2.