© 1999 by Biometrika Trust
High-derivative parametric enhancements of nonparametric curve estimators
A1 Department of Mathematics, National Taiwan University, Taipei 106, Taiwan E-mail: cheng@math.ntu.edu.tw A2 Centre for Mathematics and its Applications, Australian National University, Canberra ACT 0200, Australia E-mail: peter.hall@anu.edu.au A3 Department of Statistics, University of Adelaide, Adelaide SA 5005, Australia E-mail: bturlach@stats.adelaide.edu.au
We suggest a method for using parametric information to modify a nonparametric estimator at the level of relatively high-order derivatives. The technique represents an alternative to methods that first fit a parametric model and then adjust it. In particular, relative to a 'nonparametric estimator with a parametric start', our estimator is not biased by the differences between parametric and nonparametric fits to low-order derivatives, since we effectively remove all the parametric information about low-order derivatives and replace it by nonparametric information. Thus, we employ parametric information only when the nonparametric information. Thus, we employ parametric information only when the nonparametric information is unreliable, and do not use it elsewhere. The method has application to both nonparametric density estimation and nonparametric regression.
Key Words: Bias reduction; Curve estimation; Density estimation; Kernel regression; Local polynomial regression; Locally parametric methods; Log-polynomial model; Nonparametric regression.