Data source Validation type Group type Model classification T/S/H/U* Sensitivity/PPV** Specificity/NPV*** GC-MS 7-fold Sick 17/17/0/0 1.00/1.00 0.89/1.00 Healthy 9/0/8/1 Total 26/17/8/1 LOO Sick 17/14/3/0 0.82/0.82 0.89/1.00 Healthy 9/0/8/1 Total 26/14/11/1 Healthy 9/2/6/1 Total 26/14/8/4

Table 1: Summary of the validation analysis of the ANN models using two different validation methods. T: total members in the group; S: members in sick group; H: members of healthy group; U: Undecided by model; PPV: Positive Predictive Value; NPV: Negative Predictive Value.