Fig. 4. Relation between timing of menses and the synodic month in the remaining eight women who kept records for several years before 35 years of age.

Two of the eight women (subjects 8 and 11) exhibited a rather short cycle length and did not show any synchronization to the synodic lunar month. The other six temporarily followed the full or new moon by visual judgement (see arrows in the raster plots). The Rayleigh tests for uni- or bimodal distribution with central tendency at full or new moon confirmed the latter judgement for three of these women (subjects 9, 13, and 15) and showed a tendency (P < 0.1) for two women (subjects 1 and 14) (left P values in the raster plots). In subject 1, this tendency became significant, when only the first 15 years were included in the analysis. For subject 12, the phase relation between menses onsets and the full or new moon was rather irregular; nevertheless, menses appear to have coupled loosely to the Moon. Labeling as in Fig. 1.