Table 1.

Confusion matrix for prediction of nominal NO2 levels after COVID-19 (aC) and before COVID-19 (bC) with the conditional inference tree. The percentage of true positive classification is given per class and per total.

	aC	bC	Positive predictive value
aC	22	8	73.3%
bC	8	88	91.6%
total	30	96	87.3%