Comparison to significance scores for a test of differential expression calculated using a negative binomial model. Using the tag counts from 8 normal brain libraries versus 10 ependymoma libraries, differential expression between these two sample types was assessed using two methods. Plotted are the significance scores calculated for a negative binomial model versus a Poisson mixture model. The negative binomial (x-axis) is a p-value, so smaller values are more significant. The Poisson mixture (y-axis) is a confidence score, so larger values are more significant. Circled are two examples of SAGE tags where one model shows significance while the other does not.