= Empirical influence function
{title2=$\operatorname{EIF}_n(z)=\operatorname{IF}(z;T,F_n)$}
This plugs the <empirical distribution> into the population <influence function>. For an <M-estimator> it is $-[n^{-1}\sum_i\partial_\theta\psi(y_i,T(F_n))]^{-1}\psi(z,T(F_n))$, when this denominator is well-defined and nonzero. For functionals involving a density at a quantile, an unsmoothed empirical measure may not permit this derivative, so smoothing or an actual <sensitivity curve> is required.
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