Co-STAR results will be compared to results from the Women's Health Initiative Study of Cognitive Aging (WHISCA), a study involving 6-year longitudinal assessment of cognitive outcomes in 2969 women randomly assigned to receive active treatment (Premarin or Premarin plus medroxyprogesterone acetate) or placebo. A comparison of the Co-STAR treatment groups with the group of WHISCA participants receiving placebo will provide insights into the effects of SERMs relative to no treatment. A comparison of the Co-STAR treatment groups with WHISCA treatment groups receiving ET or ET plus progesterone will provide insights into the effects of SERMs relative to common HT treatments.