od optical density measured at 450nm normalised_od OD value normalised against plate controls od_pos sample considered negative (0) or positive (1); threshold set by finite mixture model od_jindex sample considered negative (0) or positive (1); threshold set by ROC curve, maximising Youden'd J-index od_spec sample considered negative (0) or positive (1); threshold set by ROC curve, maximising specificity od_sens sample considered negative (0) or positive (1); threshold set by ROC curve, maximising sensitivity od_EM sample considered negative (0) or positive (1); threshold set by expectation-maximisation algorithm od_vip sample considered negative (0) or positive (1); threshold set by visual inspection of the inflection point NA missing value