Re-weighting the Second Supplement on Aging to the 1994 National Health Interview Survey for Trend Analyses

by Hakan Aykan, Vicki A. Freedman, Linda G. Martin

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The Second Supplement on Aging (SOA II) to the 1994 National Health Interview Survey (NHIS) and the Supplement on Aging (SOA) to the 1984 NHIS were intended to be two comparable surveys of the elderly population 70 years of age and older. Together these surveys may be used to examine changes in a variety of measures relevant to the health and well-being of older Americans. The differences in the design and administration of the two surveys, however, could compromise their comparability and thus make it questionable to obtain unbiased estimates from studies using the SOA and the SOA II. In this study, the authors investigate the major differences and their implications. The main difference between the two surveys is that there is a time lag of 7 to 17 months between the 1994 NHIS and the SOA II, whereas the SOA was administered at the same time as the 1984 NHIS. In addition to potentially affecting comparability, this lag may result in nonrandom attrition. The authors address the issue of comparability by ensuring that the results from both surveys are generalizable to the same target population. The authors investigate the attrition in the SOA II and find the attrition nonrandom in the bivariate and multivariate analyses. The authors develop a re-weighting strategy to account for this attrition by devising weighting adjustments to the existing weighting scheme in the SOA II. The authors find that population counts using the original SOA II weights and the revised sets of weights substantially differ especially by various basic health and disability measures, even though differences in percentage distributions are not large.

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