Nothing
covc <-
function(cluster, estfun, N1, K1, NROW1, fm1) {
cluster = factor(cluster)
# Calculate the "meat" of the sandwich estimators
# call this middle to avoid partial matching
u = apply(estfun, 2, function(x) tapply(x, cluster, sum))
middle = crossprod(u)/N1
# Calculations for degrees-of-freedom corrections, followed
# by calculation of the variance-covariance estimate.
# NOTE: NROW/N is a kluge to address the fact that sandwich uses the
# wrong number of rows (includes rows omitted from the regression).
M = length(levels(cluster))
dfc = (M/(M-1)) * ((N1-1)/(N1-K1))
return(dfc * NROW1/N1 * sandwich(fm1, meat.=middle))
}
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