Raghunathan K, Layton JB, Ohnuma T, Shaw AD. Observational research using propensity scores. Adv Chronic Kidney Dis. 2016 Nov;23(6):367-72. doi: 10.1053/j.ackd.2016.11.010
Johannes CB, Crawford SL, Longcope C, McKinley SM. Bleeding patterns and changes in the perimenopause: a longitudinal characterization of menstrual cycles. Clin Consultations Obstetr Gynecol. 1996;8:9-20.