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Combining Direct and Proxy Assessments to Reduce Attrition Bias in a Longitudinal Study

Wu, Qiong PhD*; Tchetgen Tchetgen, Eric J. PhD†,‡; Osypuk, Theresa L. ScD§; White, Kellee PhD; Mujahid, Mahasin PhD; Maria Glymour, M. ScD#

Alzheimer Disease & Associated Disorders: July-September 2013 - Volume 27 - Issue 3 - p 207–212
doi: 10.1097/WAD.0b013e31826cfe90
Original Articles
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Retaining severely impaired individuals poses a major challenge in longitudinal studies of determinants of dementia or memory decline. In the Health and Retirement Study (HRS), participants complete direct memory assessments biennially until they are too impaired to complete the interview. Thereafter, proxy informants, typically spouses, assess the subject’s memory and cognitive function using standardized instruments. Because there is no common scale for direct memory assessments and proxy assessments, proxy reports are often excluded from longitudinal analyses. The Aging, Demographics, and Memory Study (ADAMS) implemented full neuropsychological examinations on a subsample (n=856) of HRS participants, including respondents with direct or proxy cognitive assessments in the prior HRS core interview. Using data from the ADAMS, we developed an approach to estimating a dementia probability and a composite memory score on the basis of either proxy or direct assessments in HRS core interviews. The prediction model achieved a c-statistic of 94.3% for DSM diagnosed dementia in the ADAMS sample. We applied these scoring rules to HRS core sample respondents born 1923 or earlier (n=5483) for biennial assessments from 1995 to 2008. Compared with estimates excluding proxy respondents in the full cohort, incorporating information from proxy respondents increased estimated prevalence of dementia by 12 percentage points in 2008 (average age=89) and suggested accelerated rates of memory decline over time.

Departments of Biostatistics

Epidemiology, Harvard School of Public Health

§Department of Health Sciences, Bouvé College of Health Sciences, Northeastern University

#Department of Society, Human Development, and Health, Harvard School of Public Health, Boston

*Harvard Center for Population and Development Studies, Harvard University, Cambridge, MA

Department of Epidemiology and Biostatistics, University of South Carolina, Columbia, SC

Department of Epidemiology, University of California at Berkeley, Berkeley, CA

Supported by the National Institutes of Health/National Institute on Aging (AG03438501) and a pilot grant from the NIA sponsored Program on Global Demography of Aging at Harvard University. The Health and Retirement Study (HRS) is sponsored by the National Institute on Aging (Grant number NIA U01AG009740) and is conducted by the University of Michigan.

The authors declare no conflicts of interest.

Reprints: M. Maria Glymour, ScD, Department of Society, Human Development and Health, Harvard School of Public Health, Kresge 617, 677 Huntington Avenue, Boston, MA 02115 (e-mail: mglymour@hsph.harvard.edu).

Received February 15, 2012

Accepted July 9, 2012

© 2013 by Lippincott Williams & Wilkins.