“…Some researchers employed physiological measurements to determine the LH surge (e.g., Ovukit: Bullivant et al, 2004;Ovusign: Gangestad et al, 2002;Clearplan: Graham, Janssen, & Sanders, 2000), measured cervical mucus (Burleson et al, 2002), or estrogen and progesterone levels (Sanders, Warner, Backstrom, & Bancroft, 1983) or their metabolites (Wilcox et al, 2004), but most studies employed backward or forward counts from Day 1 of menstruation (Table 1). Similar issues surround differences in the number of menstrual phases defined across a cycle (10 phases, Matteo & Rissman, 1984;6 phases, Bullivant et al, 2004;2 phases, Rosen & Lopez, 2009;Singh & Bronstad, 2001), the length of each phase (same length, Singh & Bronstad, 2001 or different lengths, Bullivant et al, 2004;Burleson et al, 2002), if data were broken down by cycle (Brown, Morrison, Calibuso, & Christiansen, 2008a) or averaged across women who contributed different numbers of cycles (Bullivant et al, 2004), and the number of cycles women were followed (usually only one but sometimes up to five cycles). Most researchers defined phases based on women's hormone profiles (broadly proliferative/follicular with high estrogen levels versus secretory/luteal with high estrogen and higher progesterone levels).…”