Wagstaff, Paci and van Doorslaer (1991): $$CI = (2 / \mu) \, \mathrm{cov}(h_i, R_i)$$ with \(R_i\) the fractional income rank \((rank_i - 0.5) / n\) (ties kept in input order, as the Python arm's stable sort does) and the population covariance. Negative values mean lower-income units bear more exposure.
Value
A list of class morie_envhealth_equity with
concentration_index, interpretation, n_quintiles,
exposure_mean, citation and extra.
Examples
d <- data.frame(exposure = c(30, 25, 20, 15, 10), income = 1:5)
morie_envhealth_equity(d, "exposure", "income")$concentration_index
#> [1] -0.2