The certainty was higher in the group having a pre-PET diagnosis of AD (n = 408; Figure 3A and 3B), increasing from 7.6 (SD, 1.7) to 8.2 (SD, 2.0) (P < .001), and among the patients with a pre-PET AD diagnosis having a positive tau PET scan (supportive of an AD diagnosis) where certainty increased from 8.0 (SD, 1.4) to 9.0 (SD, 0.9) (P < .001). This evidence concerns the gene MAPT and Alzheimer disease.