MAPT and Parkinson disease: For instance, the low positive predictive value of PD diagnosis, i.e., 76% [4], in the 1990s, when many PD screening surveys were conducted, and the presence of neuritic Aβ plaques or tau deposits in considerable proportions of non-demented persons [5,6] seriously undermine the validity of numerators and denominators of clinical PD and AD incidence counts respectively.