Effect of Trimming on LP III Flood Quantile Estimates

Abstract

In the fields of statistics and hydrology, a considerable amount of research has been directed toward robust methods of estimation. This paper broadly reviews these methods and presents results of the application of a specific robust estimation procedure, namely trimming, in flood frequency analysis. Using simulation, the effect of various proportions of symmetric trimming on the estimation of moments, distribution parameters, and quantiles is examined. The influence of the sample size and parent distribution parameters on the estimation performance is also investigated for several return periods and for three different fitting methods for the log-Pearson Type III distribution. While the results point to the potential usefulness of robust estimators in hydrological analysis, they also serve as a precaution that certain distribution fitting techniques may be overly robust to extreme observations in the sample (those in the tails).