Journal
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
Volume 47, Issue 5, Pages 1507-1517Publisher
OXFORD UNIV PRESS
DOI: 10.1093/ije/dyy124
Keywords
Life course; education; cognitive decline; survival bias; selection bias; collider-stratification bias; simulation
Categories
Funding
- National Institutes of Health [R13 AG030995, K99 AG053410, K01 AG050699, R01 AG051170, RF1 AG052132, U54 NS081760]
- NATIONAL INSTITUTE OF NEUROLOGICAL DISORDERS AND STROKE [U54NS081760] Funding Source: NIH RePORTER
- NATIONAL INSTITUTE ON AGING [R13AG030995, K01AG050699, R01AG051170, K99AG053410, P30AG010129, RF1AG052132] Funding Source: NIH RePORTER
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Background: The relationship between education and late-life cognitive decline is controversial. Selective survival between early life, when education is typically completed, and late life, when cognitive ageing studies take place, could attenuate effect estimates. Methods: We quantified potential survival bias (collider-stratification bias) in estimation of the effect of education on late-life cognitive decline by simulating hypothetical cohorts of 20-year-olds and applying cumulative mortality from US life tables. For each of four causal scenarios (2000 replications each), we compared the estimated versus causal effect of education on cognitive decline over 9 years, starting at age 60, 75 or 90 in random samples of n = 2000 people who survived to each age. Results: Effects of education on cognitive decline were underestimated when both education and U, another determinant of cognitive decline, influenced mortality (colliderstratification bias). The magnitude of bias was sensitive to the magnitude of the effect of U on cognitive decline and whether there was a multiplicative interaction between education and U on mortality. For example, when there was a multiplicative interaction between education and U on mortality, 95% confidence interval coverage of the causal effect ranged from 83.4% to 50.4% at age 60 and 25.8% to 0.2% at age 90. Conclusions: Selective survival could lead to underestimation of effects of education on late-life cognitive decline. Our simulations map survival bias to testable assumptions about underlying causal structures.
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