Leibenluft, Fiero, and Rubinow (1994) reviewed prior research on the menstrual cycle and mood disorders, critiquing many studies for rarely specifying which menstrual phase participants were in, while acknowledging that tracking phase for every participant adds time, effort, and cost. They recommend that mood disorder studies: (1) differentiate between menstruating, menopausal, and pre-menstrual females; (2) note that cortisol and melatonin studies commonly report the menstrual cycle as an unlikely confound; (3) account for core body temperature and plasma norepinephrine, both of which fluctuate significantly across the cycle; and (4) confirm whether and when ovulation occurred, since this is critical to accurately characterizing cycle phase.