Morley, J., Cohen, A., Silveira-Moriyama, L., Lees, A., Williams, D., Katzenschlager, R., … Duda, J. Optimizing olfactory testing for the diagnosis of Parkinson’s disease: item analysis of the university of Pennsylvania smell identification test. NPJ Parkinson’s Disease, 4, 2. https://doi.org/10.1038/s41531-017-0039-8 (Original work published 2018)