Quick proportionality calculation

ge2024_disprop.R

library(tidyverse)

dat <- tribble(~party, ~seat_share, ~vote_share,
               "Lab", 411/632, .338,
               "Con", 119/632, .237,
               "LDem", 71/632, .122,
               "SNP", 9/632, .024,
               "Ind", 6/632, 0.02,
               "Ref", 4/632, .143,
               "Green", 4/632, .068,
               "Plaid", 4/632, .007,
               "Other", 0/631, .04)

d_gall <- function(v, s) {
    sqrt(1/2 * sum((v - s)^2))
}
d_sl <- function(v, s) {
    good <- which(v > 0)
    v <- v[good]
    s <- s[good]
   sum((s - v)^2 / v)
}

gallagher <- d_gall(dat$vote_share, dat$seat_share)

sainte_lague <- d_sl(dat$vote_share, dat$seat_share)