R/sign_test.R

In nxskok/smmr: Sign test and Mood's median test

#' Sign test for given median
#' 
#' @param d a data frame
#' @param x unquoted name of column to test
#' @param med0 null median (defaults to zero)
#' @param tol (default 1e-6) how close a data value has to be to the null median to be considered equal to null median (and discarded)
#' @return list of two elements: table of values above and below null median, data frame of 1-sided and 2-sided P-values
#' 
#' @author Ken Butler, \email{butler@utsc.utoronto.ca}
#' @examples 
#' d=data.frame(z=1:10)
#' sign_test(d,z,3.5)
#' sign_test(d,z,3)
#' sign_test(datasets::mtcars, mpg, 25)
#' @importFrom rlang enquo
#' @importFrom dplyr count
#' @importFrom dplyr mutate
#' @importFrom dplyr filter
#' @importFrom rlang "!!"
#' @export
#' 
sign_test=function(d,x,med0=0,tol=1e-6) {
  x=enquo(x)
  freqs_0= d %>% mutate(y=(!!x)-med0) %>% 
    filter(abs(y)>tol) %>% count(y>0) %>% pull(n)
  v = d %>% mutate(xx=(!!x)) %>% pull(xx)
  if (length(freqs_0)==1) {
    if(v[1]>med0) {
      freqs=c(0,freqs_0)
    } else {
      freqs=c(freqs_0,0)
    }
  } else {
    freqs=freqs_0
  }
  names(freqs)=c("below","above")
  stat=freqs[1]
  n=sum(freqs)
  p_upper=sum(dbinom(0:stat,n,0.5))
  p_lower=sum(dbinom(stat:n,n,0.5))
  p_two=2*min(p_lower,p_upper)
  nn=c("lower","upper","two-sided")
  out=data.frame(alternative=nn,p_value=c(p_lower,p_upper,p_two))
  list(above_below=freqs,p_values=out)
}