Terrorist attacks and the male-to-female ratio at birth: The Troubles in Northern Ireland, the Rodney King riots, and the Breivik and Sandy Hook shootings

IntroductionMales are usually born in excess of females. The ratio is often expressed as M/F (male divided by total births). A wide variety of factors have been shown to influence M/F. Terrorist attacks reduce M/F. This study was carried out in order to ascertain whether individual terrorist attacks influenced M/F in relevant populations.MethodsThe following events were studied: the Troubles in Northern Ireland, the Los Angeles Riots (the Rodney King affair), the Breivik shooting (Norway), and the Sandy Hook shooting (Connecticut).ResultsNorthern IrelandM/F was significantly lower during the Troubles (1969–1998) than during the period before (p = 0.0006). There was a very sharp dip in 1978 (p ≤ 0.004) during this particular year of renewed violence and heavy civilian attacks.Rodney King riots—late April 1992M/F dipped significantly in August 1992, 4 months after the riots (p = 0.044).Breivik Shooting—22/07/2011M/F dipped significantly in December 2011, 5 months after the event (p = 0.004).Sandy Hook Shooting—14/12/2012M/F dipped significantly in April 2013, 4 months after the event (p = 0.009).DiscussionM/F dips follow catastrophic or tragic events if these are felt to be momentous enough by a given population. All of the above events caused significant population stress. The M/F dips noted may have been caused by population stress which is known to lead to the culling of frail/small male foetuses. The dips noted are comparable to a substantial proportion of quoted values for perinatal mortality, potentially elevating this a public health issue.Key Guidelines1.The male-to-female ratio at birth is decreased by stressful events.2.This is due to an excess of male foetal losses in established pregnancies.3.Such losses in response to acute events are transient.4.This ratio may be a useful indicator of population stress.Research Directions1.Gender ratios in populations could be routinely monitored in order to assess the impact of stressful events that may reduce the male-to-female birth ratio.