A refined index of model performance

Abstract In this paper, we develop, present and evaluate a refined, statistical index of model performance. This ‘new’ measure ( d r ) is a reformulation of Willmott's index of agreement, which was developed in the 1980s. It ( d r ) is dimensionless, bounded by − 1.0 and 1.0 and, in general, more rationally related to model accuracy than are other existing indices. It also is quite flexible, making it applicable to a wide range of model‐performance problems. The two main published versions of Willmott's index as well as four other comparable dimensionless indices—proposed by Nash and Sutcliffe in 1970, Watterson in 1996, Legates and McCabe in 1999 and Mielke and Berry in 2001—are compared with the new index.…

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  National Aeronautics and Space Administration