#Rick Chappell <> Asst. Professor, Depts. of Statistics and Human Oncology
#<> University of Wisconsin at Madison <> chappell@stat.wisc.edu
#(608) 263-5572 / 262-2733 <> take logs

samplesize.bin <- function(alpha, beta, pit, pic, rho=.5) {

# alpha is the scalar ONE-SIDED test size, or two-sided size/2
# beta is a scalar or vector of powers
# pit is the hypothesized treatment probability of success
# pic is the hypothesized control probability of success
# returns required TOTAL sample size, using arcsin transformation
# rho is the proportion of the sample devoted to treated group (0 <rho < 1) 

as <- function(x) { asin(sqrt(x))}
invas <- function(x) {(sin(x))**2}

Zalpha <- qnorm(1-alpha)
Zbeta  <- qnorm(beta)
n <- Zalpha + Zbeta
n <- n/(as(pit) - as(pic))
n <- (n**2)/(4*rho*(1-rho))
round(n+.5,0)                                       }