Fig. 1: Classification of Parkinson’s Disease (PD) based on smell.

a Distribution of likelihood ratios among PD cases and controls using the 16 odours of the University of Pennsylvania Smell Identification test (UPSIT) common to both the UK and US versions of the UPSIT identified as being associated with PD (see Table 1). b Observed detection rate according to false-positive rate (receiver operating characteristic [ROC] curve) for the 16 odours of the UPSIT identified as being associated with PD. c Distribution of likelihood ratios among PD cases and controls using the 6 odours common to both the UK and US versions of the UPSIT most strongly associated with PD (see Table 1). d ROC curve for the 6 odours of the UPSIT most strongly associated with PD. AUC, area under the receiver operating characteristic curve.