Figure 3.

Goodness of fit to the negative-binomial distribution. Quantile-quantile (Q-Q) plots of the goodness-of-fit of RNA-seq expression profiles from Pickrell [12]et al. (2010) to a negative-binomial (NB) distribution. The right y-axis indicates the quantile of the observed distribution. Columns correspond to different normalization methods where (a, d) correspond to raw un-normalized counts, (b, e) normalization with edgeR and (c, f) normalization with cqn. The top row (a, b, c) contains the Q-Q plots of the χ² goodness-of-fit statistic while the bottom row (d, e, f) contains the same Q-Q plot mapped to a normalized Z-statistic to improve the visibility of the left tail of the distribution. Independently on how count data are normalized, about 10% of the expression profiles show a substantial discrepancy to the NB distribution.