R/func_size.R

In tmnaylor/r4lineups: Statistical Inference on Lineup Fairness

#'Functional Size
#'
#'This function computes functional size (N/D), where N = number of
#'mock witnesses, & D = number of mock witnesses choosing the target
#'
#'@param lineup_vec A numeric vector of lineup choices
#'@param target_pos A scalar, representing target position in lineup. Must be declared by user
#'@return Functional size of lineup
#'@details An estimation of the number of plausible lineup members in a given lineup.
#'@references Tredoux, C. G. (1998). Statistical inference on measures of lineup fairness.
#'            \emph{Law and Human Behavior, 22}(2), 217-237.
#'
#'            Tredoux, C. (1999). Statistical considerations when determining measures of
#'            lineup size and lineup bias. \emph{Applied Cognitive Psychology, 13}, S9-S26.
#'
#'            Wells, G. L.,Leippe, M. R., & Ostrom, T. M. (1979). Guidelines for
#'            empirically assessing the fairness of a lineup. \emph{Law and Human Behavior,
#'            3}(4), 285-293.
#'@examples
#'#Data:
#'lineup_vec <- round(runif(100, 1, 6))
#'target_pos <- 3
#'
#'#Call:
#'x <- func_size(lineup_vec, target_pos)
#'x <- func_size(lineup_vec, 3)
#'
#'@export

func_size <- function(lineup_vec, target_pos){

    lineup_vec <- typecheck(lineup_vec)

    fsize <- length(lineup_vec) / sum(lineup_vec == target_pos)
    return(fsize)
}