Fig. 1

Conditional inference tree for the RD data. The rectangles at the bottom of the figure correspond to the “terminal nodes” and visually show the probabilities of DR for each path through the tree. The first node of the conditional inference tree (the “root node”) split the data according to the duration of DM (p < 0.001). Individuals with less than 24 months of DM were classified according to the MA values (interior node 2, p < 0.001), and those with values lower than 73.3 mg/L where classified as low risk for DR (terminal node 3). On the other hand, individuals with more than 24 months of DM were classified according to the papillary excavation (interior node 5, p = 0.016), where those with papillary excavation higher than 0.2 where classified as high risk for DR (terminal node 7). It is important to note that a cut-off value of 0.2 for the papillary excavation seems to be uninterpretable in a clinical point of view and it was obtained from an algorithm merely mathematical