Subjects were asked their year, month and country of birth. For SOB analyses, only those born under 25 years ago in countries that are predominately north of the Tropic of Cancer were considered. North of the Tropic of Cancer marks increased photoperiod variation in a consistent direction and a point beyond which photoperiod variation has been observed to effect reproductive behavior in non-human primates [87]. Since most of the sample (181 or 92.8%) was born north of the Tropic of Cancer, analysis was only conducted on this Northern Hemisphere sample. The 25 year age limit was employed because SOB effects have been observed to reverse with age in other studies [24], [26]–[28] and all but two subjects were under 25 in this study.
