61 Development of an algorithm to discriminate between plasmid- and chromosomal-mediated AmpC and specificity of 0.81 (95% CI=0.66–0.91) and 1.00 (95% CI=0.92–1.00), respectively (Table 2 and Table S2) Table 2. Accuracy of final decision tree model trained using the 84 E. coli strains of the training set on all datasets Dataset n Three-class model, percentage accuracy (95% CI) Two-class model, percentage accuracy (95% CI) Training set 84 0.88 (0.79–0.94) 0.90 (0.82–0.96) Validation set 1 47 0.79 (0.64–0.89) 0.91 (0.80–0.98) Validation set 2 41 0.85 (0.71–0.94) 0.85 (0.71–0.94) Figure 4. Strain selection and decision tree model based on 84 E. coli strains of the training set. The grey area corresponds to strain selection. The numbers in the coloured boxes indicate the numbers of strains classified according to the decision tree. The decision tree cut-off value for pampC is ≥6 mg/L. For the negative strains the cut-off is <0.50 mg/L. For the hyperproducer strains the cut-off is set to <6 mg/L followed by ≥0.50 mg/L. Cut-offs are based on Etest values. CTX, cefotaxime; FOX, cefoxitin. 4
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