<p>The aa at the top of each box is relative to the attributes specified at the first and second level of the trees. A, B, C and D indicate the low, moderate, high and very high bins, respectively (for more details, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065587#pone-0065587-t003" target="_blank">Table 3</a> and the “<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065587#s4" target="_blank">Materials and Methods</a>” section). Green boxes, a combination that classifies an instance as a PPI; Red boxes, a combination that classifies an instance as a no-PPI; Brown boxes, a combination that classifies an instance as a PPI or no-PPI; “?”, a combination for which an instance can not be classified, requiring classification at the next level of the tree.</p
