The probability of a male birth in humans is about .51. It has previously been noticed that lower proportions of male births are observed when offspring is conceived at times of exposure to smog, floods or earthquakes. Danish researchers hypothesised that sources of stress associated with severe life events may also have some bearing on the sex ratio. To investigate this theory they obtained the sexes of all 3,072 children who were born in Denmark between 1 January 1980 and 31 December 1992 to women who experienced the following kind of severe life events in the year of the birth or the year prior to the birth: death or admission to hospital for cancer or heart attack of their partner or of their other children. They also obtained sexes on a sample of 20,337 births to mothers who did not experience these life stress episodes. This data frame contains the data that were collected. Noticed that for one group the exposure is listed as taking place during the first trimester of pregnancy. The rationale for this is that the stress associated with the cancer or heart attack of a family member may well have started before the recorded time of death or hospital admission.
A data frame with 5 observations on the following 4 variables.
Indicator for groups to which mothers belong
Indicator for time at which severe life event occurred
Number of births
Percentage of boys born
Ramsey, F.L. and Schafer, D.W. (2002). The Statistical Sleuth: A Course in Methods of Data Analysis (2nd ed), Duxbury.
Hansen, D., Møller, H. and Olsen, J. (1999). Severe Periconceptional Life Events and the Sex Ratio in Offspring: Follow Up Study based on Five National Registers, British Medical Journal 319(7209): 548–549.
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