Shih-Fan Lin 1, DrPH. Brian K. Finch 1, Ph.D. Audrey N. Beck 1, Ph.D. Robert A. Hummer 2, Ph.D. Ryan K. Masters 3, Ph.D.

Elucidate how U.S. disability prevalence changed among older adults age 70+ using the Age-Period- Cohort (A-P-C) models. Compare (a) unadjusted and (b) socio-demographics and A-P-C adjusted trends. Examine the black-white disparity trend in late-life disability using the A-P-C models Socio-demographics and A-P-C adjusted disparity trends. Stratify by gender.

Outcome: Late-life disability ADL Disability: limitations on activities of daily living such as bathing, ambulating, and toileting. IADL Disability: limitations on instrumental activities of daily living such as shopping, writing a check, and cooking.

In the realm of demography, sociology, and epidemiology, time can be captured by three unique temporal dimensions: Age (A), Period (P), and Cohort (C). Each aspect of A-P-C has a unique contribution to the study of population health including disability.

Age is a proxy for biological processes that ultimately lead to disease, disability, and/or death. Age may also be associated with changes in status, social roles, and social position (Yang and Land 2007). Individuals’ aging processes can have differential impacts on population sub-groups (e.g. racial groups) over time.

Period or survey year, reflects changes in socio- cultural, economic, technological, medical, and environmental factors that may affect the entire population at a given time simultaneously, but perhaps not equally. For example, a drought may lead to increased food prices, which may impose greater impacts on those with lower incomes than the more well-off.

Cohort describes a unique set of individuals who are both born into a social system during a similar time period and experience similar formative social experiences over their life course. Successive cohorts that experience different historical and social conditions differ in their exposure to socioeconomic, behavioral, and environmental risk factors. The colloquial concept of generational difference is an attempt to capture the unique characteristics of distinct cohorts.

Integrated Health Interview Series (IHIS), Harmonizes National Health Interview Survey (NHIS) variables to allow consistent coding across each survey to facilitate temporal analysis. The NHIS is a repeated cross-sectional survey. Purpose: to investigate and monitor the prevalence of important health outcomes (including disability) of the civilian non-institutionalized U.S. population. Inclusion criteria: Older adults aged 70 and over. Age of 70 is the youngest common age cut point for which the disability items were inquired between the survey periods is the first NHIS survey year that the disability status was inquired.

Identification problems occur when the predicting variables in a regression are linearly dependent. There is an exact linear dependence between age, period, and birth cohort. To break the linear dependence, we group cohorts into 5-year bands. For example, individuals who were born between were collapsed into the 1900 cohort (mid-point of 1898 and 1902). PeriodAgeCohort

Unadjusted ADL/IADL disability trends: 6 separate logistic regressions in which ADL/IADL disability (dichotomous) was regressed on A-P-C separately (e.g. ADL Disability = β 0 + β 1 age). Adjusted ADL/IADL disability trends: ADL/IADL disability (dichotomous) was regressed on A-P-C simultaneously with the addition of socio-demographic variables (e.g. Adjusted ADL disability trend: ADL Disability = β 0 + β 1 age + β 2 period + β 3 cohort + β 4 race + β 5 education +……… β n income). Age was entered linearly while periods were entered as single- year dummies and cohorts were entered as 5-year bands. Omitted category for period: 1982 Omitted category for cohort: 1885

Adjusted disparity trends in ADL/IADL disability. ADL/IADL disability was regressed on A-P-C simultaneously while interacting race (black/white) with each A-P-C and controlling for socio-demographic variables (e.g. Disparity trend by cohort: ADL Disability = β 0 + β 1 race + β 2 age + β 3 period + β 4 cohort + β 5 race × cohort + β 6 education + ………β n income). Age was entered linearly and as a squared term while periods were entered as single-year dummies and cohorts were entered as 5-year bands. Omitted category for period: 1982 Omitted category for cohort: 1895

Unadjusted Trends Adjusted Trends

Unadjusted Trends Adjusted Trends

Unadjusted Trends Adjusted Trends

The unadjusted predicted probabilities of ADL and IADL disability increase substantially with age. The age effects remain strong after adjusting for period and cohort effects and socio-demographic variables. The unadjusted and adjusted periods trends show similar results – there was a substantial decline in IADL disability between 1982 and 2009 while ADL disability remained stable over the last 3 decades.

The unadjusted cohort trends for both outcomes also showed continual declines across each successive cohort; however, increasing cohort trends were evidenced in the adjusted model. More recent cohorts of U.S. older adults are becoming more disabled, net of age effect and net of changes in socio-cultural, technological, medical, economic and environmental factors captured by period effects.

Blacks are more likely to experience disability than whites. Women tend to have greater black-white disparities than men with respect to each age, period, and cohort trend and each disability outcome. The black-white disparities in IADL disability tend to be greater than the disparities in ADL disability.

For both men and women, there is a persistent increase of disparity in ADL and IADL disabilities across age. This supports the “double jeopardy hypothesis” which suggests that both minority status and aging together contribute to double disadvantages in health (disability). The double jeopardy effect seems to be more pronounced for black women than black men, especially for the ADL disability.

Although a decreasing trend of IADL disability and a steady ADL trend were observed across each period (slide #13), there is not a consistent period-based disparity trend for ADL or IADL disability. Fluctuations of disparity are greater for IADL than ADL disability. There are several dips (1984, 1995, 2000, and 2004) where blacks actually had advantages over whites on both types of disability; however, the race × period interactions for these years were not significant.

Except for a few cohort variations, the ADL disparity for both men and women remained quite stable between 1905 and 1930 cohorts. The cohort-based IADL disparity trend for men follow closely to the cohort-based ADL disparity trend. However, there is a persistent increase (except the two most recent cohorts) of IADL disparity across each successive cohort among women. This is consistent with the general increase of IADL disability across cohorts (slide #14).

ACKNOWLEDGEMENTS This project was supported by Award Number R01MD from the National Institute on Minority Health and Health Disparities (NIMHD). The content of this presentation is solely the responsibility of the authors and does not necessarily represent the official views of the NIMHD or the National Institute of Health.