A universally acceptable smoothing factor for kernel density estimates

Abstract

We define a minimum distance estimate of the smoothing factor for kernel density estimates, based on a methodology first developed by Yatracos. It is shown that if $f_{nh}$ denotes the kernel density estimate on $\mathbb{R}^d$ for an i.i.d. sample of size n drawn from an unknown density f, where h is the smoothing factor, and if $f_n$ is the kernel estimate with the same kernel and with the proposed new data-based smoothing factor, then, under a regularity condition on the kernel K, $$\sup_f \limsup_{n \to \infty} \frac{E \int | f_n - f|dx}{\inf_{h>0} E \int |f_{nh} - f|dx} \leq 3.$$ This is the first published smoothing factor that can be proven to have this property.