R/safeguard.r.r

In GiulioCostantini/safeguardpower: Safeguard Power Analysis

safeguard.r <- function(r, n, sig.level = .05, power = .8, conf = .80)
{
  if (r >= 0) alternative = "greater" else alternative = "less"
  if (conf < .5 | conf >= 1) stop ("The parameter conf must be in the interval .5<conf<1")
  rci <- r.con(rho = r, n = n, p = conf, twotailed = FALSE)
  if(sign(rci[1]*rci[2]) < 0)
  {
    warning("the safeguard r is negative: the safeguard sample size is therefore set to Inf")
    return (c("Lower_r" = rci[sign(rci) != sign(r)], "N_required" = Inf, "SSR" = Inf))
  }
  r.sg <- sign(rci[1])*min(abs(rci))
  pw <- tryCatch(pwr.r.test(n = NULL, r = r.sg, sig.level = sig.level, power = power, alternative = alternative),
               error = {function(err)
               {return(NA)}
               })
  if(all(is.na(pw)) & r.sg >= .5)
  {
    warning("the value of r is so high that it was not possible to compute a precise value of sample size. The sample size was therefore rounded to 2")
    N_required <- 2
  }
  if(all(is.na(pw)) & r.sg < .5)
  {
    warning("the safeguard r is too small: the safeguard sample size could not be computed exactly and is therefore set to Inf")
    return (c("Lower_r" = r.sg, "N_required" = Inf, "SSR" = Inf))
  }
  if(!all(is.na(pw))) N_required = ceiling(pw$n)
  SSR = N_required/n
  c("Lower_r" = r.sg, "N_required" = N_required, "SSR" = SSR)
}