The biological variation of testosterone and Sex Hormone-Binding Globulin (SHBG) in polycystic ovarian syndrome: Implications for SHBG as a surrogate marker of insulin resistance. - Jayagopal,V.; Kilpatrick,E.S.; Jennings,P.E.; Hepburn,D.A.; Atkin,S.L. (J Clin Endocrinol Metab, 2003)