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. 2015 Apr 11;8:141. doi: 10.1186/s13104-015-1062-7

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© Lazic; licensee BioMed Central. 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Mean-variance relationships for different models. A normal model assumes that the variance is constant and does not depend on the mean. A Poisson model assumes that the variance is equal to the mean. A binomial model has maximal variance at a proportion of 0.5 and progressively smaller variances on either side. The means and variances for the four experimental groups from Mehta et al. are plotted [18], and if the points fall along the line of equality then a Poisson model would be suitable. The variance is greater than the mean in this data, indicating overdispersion. Dashed line = regression line.