Confidence levels of ANN based classification. The measure of confidence of the ANN (soft decision output) is a number between 0 and 1. 0.5 is interpreted as 50% confidence, 0 and 1 as 100% true negative or 100% true positive, respectively. Based on the ANN soft decision output the spectra are placed on the curve, corresponding to their confidence level. The term “Sorted Observations” refers to the number of analysed spectra. Each observation represents one spectrum. False negative spectra are marked by a circle (with standard deviation, red line) and the false positive spectra are marked by a triangle (with standard deviation, red line). The blue lines mark the undefined spectra whose standard deviation crosses the 50% confidence decision boundary.