Assessing presence and magnitude of over-dispersion. A) The horizontal axis indicates the mean scaled count within each of the high/low response groups on the square root scale (labeled on the raw scale) and the vertical axis indicates the variation on the standard deviation (i.e. square root of the variance) within each group. Each gene is thus represented by two points, one for each response group. The green line corresponds to the Poisson assumptions, the blue line corresponds to OD Poisson assumptions, and the red line corresponds to NB assumptions, with lines constructed as described in the text. B) Local estimates of φ from the edgeR function versus per-group mean count. The shading indicates density of points in that area with darker shading representing higher density.
Oberg et al. BMC Genomics 2012 13:304 doi:10.1186/1471-2164-13-304