Fig. 1.

Overall design of the Mayo Clinic Cohort Study of Oophorectomy and Aging. The numbers of women included in the follow-up were different for parkinsonism and for cognitive impairment or dementia. The numbers for cognitive impairment or dementia were reduced because only the women who were interviewed were informative. The asterisk indicates that a total of 95 referent women underwent oophorectomy after the index year and from 1950 through 1987. Because these women were included in both cohorts, they were counted only in the oophorectomy cohort regarding vital status at follow-up (2001–006).