Shih-Fan (Sam) Lin Brian K. Finch Audrey N. Beck San Diego State University

 Black-White Disparity in Disability  Examine the black-white disparity trends in late- life disability with Age-Period-Cohort models using the cross-classified random effects model. Socio-demographic and A-P-C adjusted disparity trends. Stratify trends by gender.  Elucidate the role of aging and race in disability.  Decompose the adjusted and cohort-based disparity trend for ADL and IADL disabilities to assess the relative contribution of each sociodemographic control variable.

 Time can be captured by three unique temporal dimensions: Age, Period, and Cohort. Each aspect of A-P-C has a unique contribution to the study of population health including disability.  Most of previous studies in disparity in disability only focused on period-based or age-based trends.  There were very few research studies that examined the disability prevalence on another critical temporal dimension – birth cohort.

 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).

 Period or survey year, reflects changes in socio-cultural, economic, technological, 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 disproportionately affects those with lower incomes.

 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.  The colloquial concept of “generations” is an attempt to capture the unique characteristics of distinct birth cohorts.

 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 (Period = Age + Cohort).  To break the linear dependence, we group cohorts into 5-year bands.  For example, individuals who were born between were collapsed into the 1885 cohort (mid-point).

 Integrated Health Interview Series (IHIS),  IHIS harmonizes the National Health Interview Survey (NHIS) variables to allow consistent coding across each survey year 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 for our study  Older adults aged 70 and over. For the survey period, the disability items were only asked of those aged 70 and older (71 for 1982).  NHIS 1982 is the first survey year that the disability status is available.  Finalized sample:  Consists of 199,001 respondents 35.7% are white men 4.2% are black men 52.9% are white women 7.2% are black women.

 Dependent variables  ADL disability (yes/no)  IADL disability (yes/no)  Independent variables  Age – cohort median centered; entered linearly and as a square term  Period – year of interview  Cohort – birth year; 5-year grouping Period and cohort variables were not modeled directly, but estimates were obtained via a post-estimation strategy describe in the analysis section.  Sociodemographic controls: Dummies: race (black/white), region of residence, marital status, employment status, & BMI Continuous: education (cohort-median centered), & CPI adjusted family income (grand-mean centered).

 We fit a logistic- cross-classified random effects model for each disability outcome (ADL and IADL disabilities) and each was stratified by gender.  For each disability outcome, 2 sets (men and women) of logistic regression were performed.  For each regression:  The ADL or IADL disability (yes/no) was regressed on age (cohort-median centered) in linear and squared terms, race (black/white), and a host of sociodemographic control variables in the fixed effect portion.  We also specified the random intercept for each period and cohort. Cohort was crossed with each period and vice versa.

 For each of the four racial-gender subgroups (white men, white women, black men, and black women), the predicted probabilities of ADL/IADL disabilities were calculated separately for each A-P-C dimension while holding the rest of predicting variables at the intercept.  For example: The predicted probability of ADL disability for each cohort among black men was calculated while specifying the race variable at 1 (0=white, 1=black), sociodemographic dummy variables at the reference category (married, retired, residence at the northeast region, and normal BMI) and holding years of education at the median value of each cohort and income at the grand mean value.  The difference (black minuses white) in predicted probabilities for each age, period, and cohort and for men and women were plotted for both ADL and IADL disabilities.  To make more interpretable results of the predicted probability for age, we used the non-cohort-median- centered age and age squared model while other variables remained the same form.

 We also decomposed the age-period - adjusted cohort-based disparity trend for ADL and IADL disabilities to assess the relative contribution of each sociodemographic control variable using Fairlie’s decomposition method for nonlinear outcomes.

1. Blacks have higher predicted probability of having ADL/IADL disability compared to whites and the racial gaps tend to be larger among women than men for both outcomes.  These patterns were observed for age, period, and cohort trends. 2. The age trends show a persistent increase of disparity across age for both disability outcomes (less apparent for men).  This supports the “double jeopardy” hypothesis – both aging and minority status contribute to the poor health outcomes (i.e. ADL and IADL disabilities) for blacks at later age. 3. The period-based disparity trends for ADL disparity were flat and the IADL disparity trends were less consistent as there was a small drop of IADL disparity between 1996 and  These trends are the same for men and women. 4. The cohort-based ADL and IADL disparities declined continually across each successive cohort for both genders.  Gender differences in ADL and IADL disparities also substantially decrease with each successive cohort.  The persistent black-white disparities for both types of disability seem to almost disappear in the most recent cohort (1940).

1. Education and income persistently contributed to the ADL and IADL disparities for men and women; however, education had a more pronounced impact.  For example, in the1900 cohort, the ADL racial disparity would have been 53% smaller if black men were to have the same education profile as white men; whereas, the reduction of the disparity would have only been 36% if black men’s income profile were similar to that of white men’s. 2. Racial differences in employment status only explained a very little portion of the ADL or IADL disparity for men and women. 3. Marital status gradually became a more important contributor to the racial disparity, however, this was more salient for IADL disparity. 4. There was a remarkable decline in the importance of region of residence across the cohorts for the IADL disparity among men and women. For the ADL disparity among men and women, there seems to be an initial decline of importance of the region of residence and the trend reversed.

5. BMI does not play an important role for men regardless of the type of disability gap. 6. Among women, BMI increasingly contributed to the ADL disparity between the cohorts.  These contributions were negative: the ADL disparity between black and white women would have been larger if black women were to have the same BMI distribution as white women. 7. The contribution of BMI for the IADL disparity among women remained quite constant.