Birthday effect

[5][7] With the introduction of statistical software that can process large datasets easily, a number of state- or country-wide studies have been carried out to investigate whether birthdays have any effect on mortality.

[4] Smaller biographical studies have also shown a birthday effect within subpopulations, such as among Major League Baseball (MLB) players[7] and people with entries in the Encyclopedia of American History.

[4][11] In the US where the legal minimum drinking age is 21, there is a very large mortality rate excess on the 21st birthday and the day immediately following, almost entirely attributable to an increase in accidents.

The uneven mortality rate distribution between men and women, and between more and less successful baseball players, suggests that both may play a role in the birthday effect: people who have focused on the public sphere of life (for example, career-driven people or professional athletes) might be reminded that their glory days have passed, while those who lived more in the private sphere (such as stay-at-home parents and amateur sports players) are more aware of what they will lose in death and try to hold on.

[5][7][17] Related is the "broken promise effect", whereby a person suffering suicidal ideation will wait until a birthday or other significant event to see whether their circumstances will improve.

Vaiserman et al. have suggested that the climatic conditions at birth act as a zeitgeber that triggers internal stress and increases the chance of death.

However studies also find changes in the mortality rate in the days immediately before and after, which are unlikely to be caused by data processing anomalies, suggesting that statistical artifacts alone cannot explain the birthday effect.