Birth Order and Mortality Risk: All-Cause and Cause-Specific Trends

Kieron Barclay, Stockholm University
Martin Kolk, Stockholm University

This study used Swedish population register data to investigate the relationship between birth order and mortality risk in adulthood for Swedish cohorts born between 1938 and 1960. We investigate both all-cause mortality as well as cause-specific mortality attributable to neoplasms, cancers of the respiratory system, diseases of the circulatory system, and accidents, suicides, and events of undetermined intent. The follow-up period is from 1960 to 2007 for all-cause mortality, and from 1968 to 2007 for cause-specific mortality. Using piece-wise constant survival models, with age as the baseline hazard, the estimates are adjusted for mother’s age at the time of birth, sibship size, and cohort effects. Focusing on sibships ranging in size from two to six, we find that mortality risk in adulthood increases with later birth order. This pattern is also consistent for cause-specific mortality risk, but is particularly pronounced for mortality attributable to cancers of the respiratory system.