It is also well known that the adult brain has tremendous neural plasticity, and manipulation of hormones results in significant improvements in various cognitive domains
+(6). In the study by Dr. Hoff et al., estrogen and progesterone levels were measured on a weekly basis for 4 weeks. The resulting data were then averaged. One can wonder whether these results were statistically significant, given the large variations during women’s menstrual cycles; the range of estradiol has been reported as 50–600 pmol (Canada) or 40–260 pg/ml (U.S.) (7). More important, however, is the fact that not all estrogens are equal. Comparing endogenous estrogen with conjugated equine estrogen is not scientifically valid, since the human radioimmunoassay for 17β-estradiol does not measure levels of estrone sulfate, equilin sulfate, 17α-dihydroequilin sulfate, equilin, equilenin, 17β-dihydroequilin, or 17β-dihydroequilenin, which are all metabolic products of conjugated equine estrogen
+(7).