Counts for two tags assessed using a negative binomial model and the Poisson mixture model where one model shows significance and the other does not. The figure is divided to show separate plots of the expression level of two tags observed in 8 normal brain libraries and 10 ependymoma libraries. The x-axis is the normalized expression (count/library size*100,000) and the y-axis is divided into the two sample types. In the top plot, the negative binomial model is not significant and the Poisson mixture is significant; in the bottom plot, the situation is reversed. Light gray guide lines denote the expected expression level of the Poisson components.