R/aPrime.R

In jvcasill/lingStuff: Tools and Gems for Linguistics Related Research

#' An A prime function
#'
#' This function allows you to calculate A prime from a vector hits 
#' and a vector a false alarms.
#'
#' @param data A data frame.
#' @param h A vector of hits (0 = miss, 1 = hit).
#' @param f A vector of false alarms (0 = correct rejection, 1 = false alarm).
#' @keywords A prime
#' @export
#' @examples
#' # Create some data
#' set.seed(1); library(dplyr)
#' axb <- data.frame(subj = sort(rep(1:10, each = 20, times = 10)),
#'                   group = gl(2, 1000, labels = c("g1", "g2")),
#'                   hit = c(rbinom(1000, size = c(0, 1), prob = .8), 
#'                           rbinom(1000, size = c(0, 1), prob = .6)),
#'                   fa =  c(rbinom(1000, size = c(0, 1), prob = .3), 
#'                           rbinom(1000, size = c(0, 1), prob = .4))
#' )
#' 
#' # Calculate A' on entire data frame
#' aPrime(axb, hit, fa)
#' 
#' # Calculate A' for each subject
#' # by group, plot it, and run a 
#' # linear model
#' axb %>%
#'   group_by(subj, group) %>%
#'   summarize(ap = aPrime(., hit, fa)) %T>%
#'  {
#'   plot(ap ~ as.numeric(group), data = ., 
#'        main = "A' as a function of group", xaxt = "n", 
#'        xlab = "Group", ylab = "A'")
#'   axis(1, at = 1:2, labels = c("g1", "g2"))
#'   abline(lm(ap ~ as.numeric(group), data = .), col = "red")
#'  } %>%
#'  lm(ap ~ group, data = .) %>%
#'  summary()

aPrime <-function(data, h, f){
    if(!is.data.frame(data)) {
    stop('I am so sorry, but this function requires a dataframe\n',
         'You have provided an object of class: ', class(data)[1])
    }

    # Make columns of dataframe available w/o quotes
    arguments <- as.list(match.call())
    hits = eval(arguments$h, data)
    fas = eval(arguments$f, data)

    hRate = mean(hits)
    faRate = mean(fas) 
    if(hRate >= faRate)
      {
        ap <- .5 + (((hRate - faRate) * (1 + hRate - faRate)) / ((4 * hRate) * (1 - faRate)))
      } else if(hRate < faRate)
      {
        ap <- .5 - (((faRate - hRate) * (1 + faRate - hRate)) / ((4 * faRate) * (1 - hRate)))
      }
      return(ap)
}