The NEO-FFI is a reliable measure of premorbid personality in patients with probable Alzheimer's disease.

Aim: To assess the inter-informant reliability, intra-informant reliability and internal consistency of the NEO-FFI as a measure of premorbid personality in patients with Alzheimer's Disease (AD).
Subjects: One hundred and five persons with NINCDS-ADRDA probable AD for the assessment of inter-informant reliability and internal consistency, and 30 for the assessment of intra-informant reliability.
Methods: Premorbid personality was rated retrospectively by close relatives remembering the patient as he/she had been when aged in his/her forties. One hundred and five AD patients were rated by two separate informants. Thirty AD patients were rated by the same informant on separate occasions one year apart.
Results: Inter-informant reliability for the five domain scores of the NEO-FFI was shown to range from fair to good when measured using the single measure Intraclass Correlation Co-efficient (ICC) (0.52-0.64), and to range from good to excellent when measured using the average ICC (0.68-0.78). Intra-informant reliability for four out of the five domains was shown to be excellent when measured using the single ICC (0.81-0.92), and good for the remaining domain (0.72). Intra-informant reliability was found to be excellent for all five domains when measured using the average ICC (0.84-0.96). Internal consistency of the five domains was good.
Conclusions: The NEO-FFI can be used reliably to measure premorbid personality in patients with probable AD. It may be useful to maximise reliability by using a mean domain score based on questionnaires completed by two or more informants who knew the patient well earlier in life.