For nine parings of variances in the measurement noise and humidity, Fig. also shows a typical instance (the one giving the median F1 score among the 100 instances) of the SVDD decision boundary, test data, and confusion matrix. The pseudo-elliptical regions over which the sensor response vectors are scattered (i) elongate as σ H 2 O increases, as water adsorbs strongly and variance in its concentration tends to dominate the variance in the responses and (ii) spread isotropically as σ m increases. At the largest values of σ H 2 O and σ m , many responses to normal conditions fall outside of the decision boundary (false positives), and many responses to anomalous conditions fall inside of the decision boundary (false negatives).