Accuracy of p-value estimations. To examine the accuracy of our p-value estimates, we compared the empirical p-value (computed from the observed distribution of scores) to p-values computed using either the exact method described above (black points) or Gaussian approximation (gray points). The scores represent the simple score at a distance of 0.1 substitutions per site calculated using the Gcn4p matrix from SCPD . Other models and matrices produce similar results.
Moses et al. Genome Biology 2004 5:R98 doi:10.1186/gb-2004-5-12-r98