Changes in the prevalence of cognitive impairment among older Americans, 1993-2004: Overall trends and differences by race/ethnicity and socioeconomic status
Research indicates that the health of the older population in the United States, as measured by most dimensions, has improved over the past two decades. Population-level changes in health have been attributed to increases in education and income and improvements in the treatment and control of disease. Recent research suggests that rates of cognitive impairment have declined as well; however, results have been inconsistent and most studies have included only two time points in the analysis. This project used data from six waves of the Health and Retirement Study to achieve the following aims: 1) determine if the prevalence of cognitive impairment among older adults declined from 1993 to 2004, and 2) determine if the pattern of change in cognitive impairment was consistent across racial/ethnic and socioeconomic groups. Analyses investigated whether changes in demographic, socioeconomic, and health status and behavior variables contributed to overall and group-specific trends. Sampling weights applied to each wave of data enabled merged waves to represent comparable cross-sections of the community-dwelling older population in the United States in each respective year of study. Logistic regression analyses employing cognitive impairment as the dependent variable and a time trend variable as the key independent variable were used to analyze trends. Results showed an annual decline in the prevalence of cognitive impairment of -3.4% per year, adjusting for changes in the age and gender distributions of the population as well as prior test exposure. Increases in educational attainment in the population accounted for the trend. Racial/ethnic and socioeconomic disparities in the prevalence of cognitive impairment decreased considerably between 1993 and 2004. Declines in the prevalence of cognitive impairment were greater for blacks and Hispanics compared to whites and for lower education and wealth groups compared to more advantaged groups. Overall and group-specific trends did not appear to be due to selection bias resulting from changes in rates of mortality or attrition of HRS respondents over time. Improvements in the socioeconomic status of the population have contributed to declines in the prevalence of cognitive impairment among older adults—particularly blacks and Hispanics—in the United States.