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The Area Under the Disease Progress Stairs: Calculation, Advantage, and Application

April 2012 , Volume 102 , Number  4
Pages  381 - 389

Ivan Simko and Hans-Peter Piepho

First author: U.S. Department of Agriculture-Agricultural Research Service, Crop Improvement and Protection Research Unit, 1636 East Alisal Street, Salinas, CA 93905; and second author: Institut für Kulturpflanzenwissenschaften, Universität Hohenheim, Fruwirthstrasse 23, D-70593 Stuttgart, Germany.

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Accepted for publication 16 November 2011.

The area under the disease progress curve (AUDPC) is frequently used to combine multiple observations of disease progress into a single value. However, our analysis shows that this approach severely underestimates the effect of the first and last observation. To get a better estimate of disease progress, we have developed a new formula termed the area under the disease progress stairs (AUDPS). The AUDPS approach improves the estimation of disease progress by giving a weight closer to optimal to the first and last observations. Analysis of real data indicates that AUDPS outperforms AUDPC in most of the tested trials and may be less precise than AUDPC only when assessments in the first or last observations have a comparatively large variance. We propose using AUDPS and its standardized (sAUDPS) and relative (rAUDPS) forms when combining multiple observations from disease progress experiments into a single value.

This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 2012.