Ytterstad E, Brenn T
Institutt for matematiske realfag.
Tidsskr Nor Laegeforen. 1997 Mar 20;117(8):1098-101.
The variation in the daily numbers of births across month, day of week, phase of the moon and maternity leave entitlements have been studied for all births in Norway between 1989 and 1993, a total of 302,209 newborn children. The number of births was highest in the spring and lowest in November and December. A secondary birth maximum was observed in September, possibly related to activities during Christmas and New Year celebrations nine months before. Furthermore, births were least numerous at weekends and were concentrated in the middle of the week. This pattern probably reflects less active obstetric intervention at weekends. The number of births does not seem to vary with phase of the moon. At the time of the latest, and largest increase in national birth maternity leave entitlements, fewer births occurred in the days before and correspondingly more births in the days immediately after the date when the change came into force.
针对1989年至1993年挪威所有出生情况（共计302,209名新生儿），研究了每月、每周的日期、月相以及产假权益对每日出生人数的影响。春季出生人数最多，11月和12月最少。9月出现了二次出生高峰，这可能与九个月前圣诞节和新年庆祝活动期间的行为有关。此外，周末出生人数最少，集中在一周的中间几天。这种模式可能反映出周末产科干预活动较少。出生人数似乎并不随月相变化。在国家生育产假权益最近一次也是最大幅度增加时，在权益变更生效日期前几天出生人数减少，而在生效日期后紧接着的几天出生人数相应增加。
