Estimating risks in declining populations with poor data

Census data on endangered species are often sparse, error-ridden, and confined to only a segment of the population. Estimating trends and extinction risks using this type of data presents numerous difficulties. In particular, the estimate of the variation in year-to-year transitions in population size (the “process error” caused by stochasticity in survivorship and fecundities) is confounded by the addition of high sampling error variation. In addition, the year-to-year variability in the segment of the population that is sampled may be quite different from the population variability that one is trying to estimate. The combined effect of severe sampling error and age- or stage-specific counts leads to severe biases in estimates of population-level parameters. I present an estimation method that circumvents the problem of age- or stage-specific counts and is markedly robust to severe sampling error. This method allows the estimation of environmental variation and population trends for extinction-risk analyses using corrupted census counts—a common type of data for endangered species that has hitherto been relatively unusable for these analyses.

The effects of health changes on projections of health service needs for the elderly population of the United States

The 1982–1994 National Long-Term Care Surveys indicate an accelerating decline in disability among the U.S. elderly population, suggesting that a 1.5% annual decline in chronic disability for elderly persons is achievable. Furthermore, many risk factors for chronic diseases show improvements, many linked to education, from 1910 to the present. Projections indicate the proportion of persons aged 85–89 with less than 8 years of education will decline from 65% in 1980 to 15% in 2015. Health and socioeconomic status trends are not directly represented in Medicare Trust Fund and Social Security Administration beneficiary projections. Thus, they may have different economic implications from projections directly accounting for health trends. A 1.5% annual disability decline keeps the support ratio (ratio of economically active persons aged 20–64 to the number of chronically disabled persons aged 65+) above its 1994 value, 22:1, when the Hospital Insurance Trust Fund was in fiscal balance, to 2070. With no changes in disability, projections indicate a support ratio in 2070 of 8:1—63% below a cash flow balance.

Changes in the prevalence of chronic disability in the United States black and nonblack population above age 65 from 1982 to 1999

Survey evidence through the early 1990s generally suggests a reduction in disability in the elderly population of the United States. Because the evidence is not fully consistent, several authors have speculated about whether disability declines will continue. This paper reports results from the 1999 National Long-Term Care Survey on disability trends from 1982 through 1999. It is found that disability continued to decline in the 1994 to 1999 period, and that the decline was greater in the 1990s than in the 1980s. The disability decline from 1982 to 1989 was 0.26% per year, from 1989 to 1994 it was 0.38% per year, and from 1994 to 1999 it was 0.56% per year. In addition, disability declined by a greater percentage for blacks than for nonblacks over the 1989 to 1999 period.