Figure 2

Effect of set size bias on mutual information. In both graphs, the y-axis represents the measured mutual information (MI) between two sets of influenza A PB2 protein sequences, comprising human and avian sequences respectively. The x-axis represents the size ratio Nh/Na, where Nh and Na are the sequence count in the human and avian sets respectively. A) Changes in MI at selected alignment sites as Nh is varied (Na = 719). MI values fall rapidly as the ratio decreases, especially at sites with high MI. B) Each data point is computed by averaging the MI obtained by comparing the human set with 200 random subsampled sets of avian sequences with the same sequence count. The estimated MI values remain stable up to a size ratio of approximately 1:10. At very low ratios, increased sampling errors due to small set size tend to lower the reliability of the estimate.