R/enp.R

In politicsR: Calculating Political System Metrics

#' The Effective Number of Parties Index
#'
#'`enp()` calculates the number of Effective Political Parties according to the formula proposed by Laakso and Taagepera (1979).
#'
#' @param x (\code{numeric}). A numeric vector in the form of a proportion of votes or seats. The vector should between from 0 to 1.
#'
#' @return
#'
#' A value corresponding to the number of effective parties. Normally we deprecate the fraction in the analysis, leaving only the integer.
#'
#' @references
#'
#' Laakso, M., & Taagepera, R. (1979). “Effective” Number of Parties: A Measure with Application to West Europe. Comparative Political Studies, 12(1), 3–27. https://doi.org/10.1177/001041407901200101
#'
#'
#' @import utils
#' @export
#' @examples
#'
#'  enp(c(0.2, 0.3, 0.5))
#'

enp <- function(x){

  test_numeric(x)

  enp <- 1 / hh(x)

  return(enp)
}