R/nclass.ss.R

In MatchingFrontier: Computation of the Balance - Sample Size Frontier in Matching Methods for Causal Inference

# Taken verbatim from the package 'cem'
nclass.ss <-
function (x) 
{
    N <- 2:100
    C <- numeric(length(N))
    D <- C
    for (i in 1:length(N)) {
        D[i] <- diff(range(x))/N[i]
        edges = seq(min(x), max(x), length = N[i])
        hp <- hist(x, breaks = edges, plot = FALSE)
        ki <- hp$counts
        k <- mean(ki)
        v <- sum((ki - k)^2)/N[i]
        C[i] <- (2 * k - v)/D[i]^2
    }
    idx <- which.min(C)
    N[idx]
}