Article Type:
Research Article

Some Comments on the Evaluation of Model Performance

Cort J. Willmott Center for Climatic Research, Department of Geography, University of Delaware, Newark, Del. 19711

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Online Publication:
01 Nov 1982
Print Publication:
01 Nov 1982
DOI:
https://doi.org/10.1175/1520-0477(1982)063<1309:SCOTEO>2.0.CO;2
Page(s):
1309–1313
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Quantitative approaches to the evaluation of model performance were recently examined by Fox (1981). His recommendations are briefly reviewed and a revised set of performance statistics is proposed. It is suggested that the correlation between model-predicted and observed data, commonly described by Pearson's product-moment correlation coefficient, is an insufficient and often misleading measure of accuracy. A complement of difference and summary univariate indices is presented as the nucleus of a more informative, albeit fundamentally descriptive, approach to model evaluation. Two models that estimate monthly evapotranspiration are comparatively evaluated in order to illustrate how the recommended method(s) can be applied.

Quantitative approaches to the evaluation of model performance were recently examined by Fox (1981). His recommendations are briefly reviewed and a revised set of performance statistics is proposed. It is suggested that the correlation between model-predicted and observed data, commonly described by Pearson's product-moment correlation coefficient, is an insufficient and often misleading measure of accuracy. A complement of difference and summary univariate indices is presented as the nucleus of a more informative, albeit fundamentally descriptive, approach to model evaluation. Two models that estimate monthly evapotranspiration are comparatively evaluated in order to illustrate how the recommended method(s) can be applied.

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