The difference between the approximate iGLASS correction (Equation 19) and the exact iGLASS correction (Equation 3). Each pixel in the heatmap shows the difference for a given divergence time τAB, a given number of lineages sampled per taxon, and a given number of loci. Within each block corresponding to a number of loci, the numbers of lineages sampled from each taxon at each locus are, from left to right, (nA, nB) = (1,1), (1,2), (1,3), (1,4), (2,2), (2,3), (2,4), (3,3), (3,4), and (4,4), where nA is the number of lineages sampled from taxon A and nB is the number sampled from taxon B.