sd <- function(x) sqrt(var(x))
logit <- function(x) log( x/(1-x))
ilogit <- function(x) {
  o <- is.na(x)
  if(any(o)){
    cat("WARNING: NA in ilogit. Assigning 0 or 1 at random\n")
    ret <- rep(NA,length(x))
  }
  else {
    ret <- exp(x)/(1+exp(x))
    if(any(exp(x)==Inf)) ret[exp(x)==Inf] <- 1
  }
  ret
}