Comparison between different motifs in P. falciparum , using the Pearson correlation between their density profiles . Each point corresponds to a gene and represents a pair of density estimates (one for each motif). The left figure suggests that the AAGACA and TAGACA sequences belong to the same motif (WAGACA), as their density profiles have a Pearson correlation coefficient of 0.94. In contrast, the TAGACA and TACACA sequences have clearly different density profiles (Pearson coefficient of 0.54), despite the fact that they differ by only one nucleotide, as shown in the right figure. The densities are estimated using 200 neighbors for each gene and are expressed as a z-score (see motif density in Material and methods).