Browsing by Subject "Cohort"

Now showing 1 - 3 of 3
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    Dementia and Mild Cognitive Impairment: Epidemiologic Research of Risk Factors
    (2019-07) George, Kristen
    Dementia and mild cognitive impairment (MCI) are often caused by progressive and irreversible pathologic brain changes. Alzheimer’s disease, cerebrovascular disease, and Lewy body-related diseases are the most common causes with many individuals having mixed etiologies. Characterizing risk factors for dementia and MCI is complex due to overlapping etiologies, long latency periods, and the influence of cognitive reserve. While major risk factors including advanced age, hypertension, and the ApoE4 allele have been identified, further investigation of early- and mid-life risk factors is needed. Using data from the Atherosclerosis Risk in Communities (ARIC) Neurocognitive Study, we examined prospectively risk factors for dementia and MCI. In the first manuscript, we assessed the association between life course socioeconomic status (LC-SES) and dementia and MCI. Low individual-level LC-SES was associated with an increased risk of dementia. Low individual-level economic factors of LC-SES (e.g. income, home ownership) were associated with increased risk of dementia independent of educational attainment. However, neighborhood-level LC-SES was not associated with risk of dementia or MCI. The second manuscript assessed the association between thyroid dysfunction (measured via autoimmune thyroid disease (AITD) and thyroid hormone levels) and risk of dementia and MCI. We found no association between AITD and dementia and MCI. Subclinical hypothyroidism was associated with a lower risk of dementia while overt hyperthyroidism, particularly with very elevated serum FT4 hormone levels, was associated with an increased risk of dementia compared to euthyroid participants. The third manuscript examined the association between lifetime history of migraine symptoms and risk of dementia and MCI. Despite published evidence of brain abnormalities in migraineurs, which might lead to cognitive impairment, we found no association between migraine and dementia and MCI. This dissertation extends our understanding of risk factors for cognitive impairment underscoring the importance of early- and mid-life exposures on late-life risk of dementia and MCI.
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    Returns to human capital and explaining the recent decline of married women's labor supply: a cohort approach
    (2013-06) Park, Seonyoung
    This dissertation emphasizes the importance of a cohort approach in dealing with some important issues in the education and the macro labor market. Essay One investigates the effects of changes in various determinants of labor supply on the dramatic changes from the older (the 1950s and earlier) cohorts to the younger (the 1960s and later) cohorts in life-cycle labor supply behavior, and ultimately provides a model-based quantitative explanation of the recent decline in the aggregate labor supply of married women. On the basis of the Current Population Survey data, it first documents that, while life-cycle labor supply profiles are bell-shaped for the older cohorts, they are roughly flat for the younger cohorts, and from the mid-thirties of the life-cycle, the younger cohorts continue to supply less labor than the 1950s cohort does. Then, in a life-cycle model of women's labor supply, the behavioral changes are explained by a combination of changes in various labor supply determinants, with the opportunity cost of childbearing being the dominant contributor. A calibration of the model demonstrates that of the 3.32 percentage points of married women's aggregate labor supply, 67 percent is explained by the increased opportunity cost for the younger cohorts, and the rest is accounted for by a combination of changes in the tax code, business cycle conditions, and preferences, among others. Essay Two focuses on how returns change as individuals increase human capital investment over the course of their work career. On the basis of those respondents in the National Longitudinal Survey of Youth (NLSY) who change jobs with an intervening period of education reinvestment, the conventional assumption of linearity of log wages in years of schooling is strongly rejected. The estimated marginal rate of return generally rises in the former education level, and reaches the maximum at 15 years of the former level (therefore 16 years of education after reinvestment), where an additional year of investment is associated with a rise in real hourly rate of pay by approximately 20 percent. The current cohort-based evidence is more helpful than existing evidence from cross-sectional data to individuals making schooling decisions.
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    Trying to Fit In: Barriers to Degree Completion for Part-Time Graduate Students
    (2016-05) Mollen, Christine
    This research explores factors that affect the persistence of part-time graduate students and how the part-time students at one large research university experience moving through their programs. Data collected though a survey administered to full- and part-time graduate students helped illustrate areas of struggle for the part-time graduate student population. Although all graduate students experience barriers to degree completion, part-time graduate students at ‘traditional’ research institutions often follow a non-traditional path to degree completion and therefore face increased and unique barriers to completing their degrees, different from their undergraduate and full-time graduate counterparts.