# This R code computes sample sizes needed 
# to obtain equivalence tests for comparing
# two success rate with specified power values. 
    
# This code is posted in the file power2e.sas  

# Specify the probability of success 
# for the first population (p1)       
  p1 <- .70 

# Specify upper bound on relative 
# risk   
  rrb <- 1.2

# Enter power values    
  power <- c(.8, .9) 

# Enter relative risk for some
# alternatives

  rra <- c(1.05, 1.10)

# Enter the type I error level

  alpha <- .05         
  np <- length(rra)
  
# Cycle across alternatives

  for(i2 in 1:np) {
     pa <- qnorm(1-alpha)*sqrt(1+1/rra[i2])
     pb <- qnorm(power)*sqrt(1+1/rrb)
     size <- ((pb+pa)/log(rrb/rra[i2]))^2
     size <- ceiling(size)

     cat("\n \n Sample sizes for equivalence test",
       "\n \n  p1=",p1,"RR=",rrb, "True RR", rra[i2], "alpha=",
       alpha,"power=", power,
    "\n \n                           Sample sizes: " , size, "\n") 

  }