Scarring In Utero: An Attempt to Validate With Data Unconfounded by Migration and Medical Care.

Abstract

"Scarring in utero" posits that populations exposed to injurious stressors yield birth cohorts that live shorter lives than expected from history. This argument implies a positive historical association between period life expectancy (i.e., average age at death in year t) and cohort life expectancy (i.e., average lifespan of persons born in year t). Tests of the argument have not produced consistent results and appear confounded by autocorrelation, migration, and access to medical care. Here we test whether, as predicted by scarring in utero, sex-specific period and cohort life expectancy appear positively related among Swedes born from 1751 through 1800. If scarring has ever influenced longevity, we should detect signals of its effects in these cohorts because, unlike other populations with known life span, they aged in place and unlikely benefitted from increased access to efficacious medical care. We use Box-Jenkins methods to control autocorrelation and measure associations. Contrary to the scarring hypothesis, we find an inverse association between period and cohort life expectancy. Our findings imply that, among males, variation in injurious stress on the population predicted changes in cohort life span ranging from a gain of approximately 67 weeks to a loss of about 45 weeks of life and among females from a gain of approximately 68 weeks to a loss of about 38 weeks of life. Epidemiologists trying to understand and explain temporal variation in cohort life expectancy should view the scarring argument with greater skepticism than currently found in the literature.