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BBD—Computer Software for Fitting the Beta-Binomial Distribution to Disease Incidence Data. L. V. MADDEN, Department of Plant Pathology, Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691. G. HUGHES, Institute of Ecology and Resource Management, University of Edinburgh, West Mains Road, Edinburgh EH9 3JG, Scotland, UK. Plant Dis. 78:536-540. Accepted for publication 5 January 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0536.

A software program for DOS-based personal computers was developed to fit the beta-binomial distribution to the frequency of incidence of disease. The beta-binomial is a discrete distribution, which is appropriate for describing aggregated or clustered binary data such as incidence. Variance-ratio and C(α ) tests are performed to determine if there is evidence that incidence is aggregated. The program then calculates distribution parameters and their standard errors using a maximum likelihood procedure, determines the expected values of the distribution, and calculates a chi-square goodness-of-fit lest. For comparison purposes, the program fits the binomial distribution to the same data. The software and a detailed user's manual are available free from either author.