Influence of the Super Bowl on the United States birth sex ratio

Abstract

IntroductionMany factors have been shown to influence the male to female ratio at birth (M/T). Celebrations increase M/T nine months later, putatively due to elevated coital rates. The Super Bowl (SBS) is consistently held in the first Sunday in February. This study was carried out in order to ascertain whether SBS results in a rise in M/T nine months later, and whether any such changes are influenced by race and census region. MethodsBirths were studied for the period 2003–2015. Seasonality adjustment was applied in order to identify true outlier values over and above those due to natural seasonal M/T variation. ResultsThis study analysed 53,105,069 births. M/T was elevated in all regions, for all races for 11/2006, 9/2009, 10/2009, 10/2010, 12/2010, 11/2011, 11/2013 and 12/2013. A similar effect is observed in the West Region for all births. For the various ethnic groups, the effect is strongest for Whites in regions Northeast, South and West, and for Black/African American births in regions Midwest and South. DiscussionEvents which increase coital activity elevate M/T nine months later as M/T follows a U-shaped regression on cycle day of insemination, with male conceptions occurring more frequently at the beginning (and end) of the menstrual cycle. SBS is a significant annual celebratory event in contemporary American culture. It is possible that increased coital rates during this period (perhaps due to a combination of celebration and inebriation) may result in the M/T rises nine months later observed in this study.