(Log) p-values of real sequence data under null hypothesis of no overdispersion against mean expression levels of each sequence. (Log) p-values of real sequence data under the null hypothesis of no overdispersion and alternative hypothesis of overdispersion. We acquire these for each sequence by performing likelihood-ratio tests on the fit of a Poisson model and an alternative negative binomial model, allowing for both differences in library size and between the two sample types. Although a number of sequences show no significant variation from the Poisson model, a substantial number show very significant variation. The sequences for which overdispersion is particularly significant are those with high mean expression levels, as these are the sequences for which overdispersion can most easily be detected.