Original articleInstrumental variable approaches to identifying the causal effect of educational attainment on dementia risk
Section snippets
Methods
The Health and Retirement Study (HRS) is a national, longitudinal study of individuals 50 years of age or older and their spouses. The first survey wave was collected in 1992, with biennial interviews (or proxy interviews for decedent participants) available through 2010. New cohorts were added in 1993, 1998, 2004, and 2010. We used follow-up data from 1998–2010 and includes individuals from all enrollment cohorts except 2010. Survey response rates ranged from 70% to 82%, and retention rates
Results
Table 1 shows the demographics of the analytic sample used for the two IV analyses. Using the 1980 census, 5% sample in the first stage, compulsory schooling laws (CSLs), school to work laws (CSL-w), and school characteristics were significantly associated with years of schooling. F statistics, an indication of the strength of the instruments for the excluded instrument, were well above 10 (Table 2). The linear regression coefficients for the effects of CSLs and school characteristics on years
Discussion
The IV estimates indicate that education lowers dementia probability. These results are consistent with previous IV literature reporting a protective effect of education on cognitive function [10], [11], [12]. Education may be an indicator of cognitive reserve, with higher educational attainment indicating larger reserve to delay the onset of dementia [27], [28].
In the IV analyses, we used state of birth and year of birth to classify the compulsory schooling required for each participant. There
Acknowledgments
E.J.T.T.’s work was funded by the National Institutes of Health (NIH) grants AI113251 and ES020337. S.E.G.’s work was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development
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None of the authors declare any conflicts of interest.