The age at baseline assessment is calculated from subtracting the date of birth from the date of the baseline assessment and dividing by days per year (365.25).

The date of the baseline assessment is defined as the the first valid date in the following hierarchy:

1. cognitive date
2. clinical evaluation date (neurological exam, med hx, meds)
3. interview date
4. DCF date (diagnostic classification form)
5. neuropsychologist impression date