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Summary A wide variety of statistical techniques involve the choice of a prescription and smoothing parameter for modifying an unsmoothed estimator towards some ultrasmooth solution. The basic common structure is illustrated by multinomial smoothing, nonparametric density estimation, linear and nonparametric regression, the solution of integral equations and image processing. Possible cross-fertilization among the different areas of application is suggested.
D. M. Titterington (Thu,) studied this question.