John R. Wilmoth

Life-long sustained mortality advantage of siblings of centenarians

Although survival to old age is known to have strong environmental and behavioral components, mortality differences between social groups tend to diminish or even disappear at older ages. Hypothesizing that surviving to extreme old age entails a substantial familial predisposition for longevity, we analyzed the pedigrees of 444 centenarian families in the United States. These pedigrees included 2,092 siblings of centenarians, whose survival was compared with 1900 birth cohort survival data from the U.S. Social Security Administration. Siblings of centenarians experienced a mortality advantage throughout their lives relative to the U.S. 1900 cohort. Female siblings had death rates at all ages about one-half the national level; male siblings had a similar advantage at most ages, although diminished somewhat during adolescence and young adulthood. Relative survival probabilities for these siblings increase markedly at older ages, reflecting the cumulative effect of their mortality advantage throughout life. Compared with the U.S. 1900 cohort, male siblings of centenarians were at least 17 times as likely to attain age 100 themselves, while female siblings were at least 8 times as likely.

Rectangularization revisited: Variability of age at death within human populations*

Rectangularization of human survival curves is associated with decreasing variability in the distribution of ages at death. This variability, as measured by the interquartile range of life table ages at death, has decreased from about 65 years to 15 years since 1751 in Sweden. Most of this decline occurred between the 1870s and the 1950s. Since then, variability in age at death has been nearly constant in Sweden, Japan, and the United States, defying predictions of a continuing rectangularization. The United States is characterized by a relatively high degree of variability, compared with both Sweden and Japan. We suggest that the historical compression of mortality may have had significant psychological and behavioral impacts.

Deceleration in the age pattern of mortality at olderages

The rate of mortality increase with age tends to slow down at very old ages. One explanation proposed for this deceleration is the selective survival of healthier individuals to older ages. Data on mortality in Sweden and Japan are generally compatible with three predictions of this hypothesis: (1) decelerations for most major causes of death; (2) decelerations starting at younger ages for more “selective” causes; and (3) a shift of the deceleration to older ages with declining levels of mortality. A parametric model employed to illustrate the third prediction relies on the distinction between senescent and background mortality. This dichotomy, though simplistic, helps to explain the observed timing of the deceleration.

Demography of longevity: past, present, and future trends.

Life expectancy at birth has roughly tripled over the course of human history. Early gains were due to a general improvement in living standards and organized efforts to control the spread of infectious disease. Reductions in infant and child mortality in the late 19th and early 20th century led to a rapid increase in life expectancy at birth. Since 1970, the main factor driving continued gains in life expectancy in industrialized countries is a reduction in death rates among the elderly. In particular, death rates due to cardiovascular disease and cancer have declined in recent decades thanks to a variety of factors, including successful medical intervention. Based on available demographic evidence, the human life span shows no sign of approaching a fixed limit imposed by biology or other factors. Rather, both the average and the maximum human life span have increased steadily over time for more than a century. The complexity and historical stability of these changes suggest that the most reliable method of predicting the future is merely to extrapolate past trends. Such methods suggest that life expectancy at birth in industrialized countries will be about 85-87years at the middle of the 21st century.

A new method for estimating smoking-attributable mortality in high-income countries

BACKGROUND Cigarette smoking is responsible for a massive loss of life in both developed and developing countries. This article develops an alternative to the Peto-Lopez method for estimating the number or fraction of smoking-attributable deaths in high-income countries. METHODS We use lung cancer death rates as an indicator of the damage caused by smoking. Using administrative data for the population aged > or =50 years from 20 high-income countries in the period from 1950 to 2006, we estimate a negative binomial regression model that predicts mortality from causes other than lung cancer as a function of lung cancer mortality and other variables. Using this regression model, we estimate smoking-attributable deaths based on the difference between observed death rates from lung cancer and expected rates among non-smokers. RESULTS Combining the estimated number of excess deaths from lung cancer with those from other causes, we find that among males in 1955 the smoking-attributable fraction was highest in Finland (18%); among women, no country exceeded 1%. By 2003, Hungary had the highest fraction of smoking-attributable deaths among males (32%), whereas the USA held that position among women (24%). Our estimates are remarkably similar to those produced by the Peto-Lopez method, a result that supports the validity of each approach. CONCLUSIONS We provide a simple and straightforward method for estimating the proportion of deaths attributable to smoking in high-income countries. Our results demonstrate that smoking has played a central role in levels, trends and international differences in mortality over the past half century.

Are Mortality Rates Falling at Extremely High Ages? An Investigation Based on a Model Proposed by Coale and Kisker

It is known that further mortality reductions in industrialized countries depend heavily on trends in mortality rates at the oldest ages. In this article, a model proposed by Coale and Kisker is used to investigate mortality trends at the extreme old age of 110 years. The most important conclusions are that (1) the form of the model proposed by Coale and Kisker fits observed mortality schedules very well indeed, and (2) the trend in mortality rates at extremely high ages has apparently been flat for men, but may have declined slightly for women during this century.

Understanding Global Trends in Maternal Mortality

CONTEXT Despite the fact that most maternal deaths are preventable, maternal mortality remains high in many developing countries. Target A of Millennium Development Goal (MDG) 5 calls for a three-quarters reduction in the maternal mortality ratio (MMR) between 1990 and 2015. METHODS We derived estimates of maternal mortality for 172 countries over the period 1990-2008. Trends in maternal mortality were estimated either directly from vital registration data or from a hierarchical or multilevel model, depending on the data available for a particular country. RESULTS The annual number of maternal deaths worldwide declined by 34% between 1990 and 2008, from approximately 546,000 to 358,000 deaths. The estimated MMR for the world as a whole also declined by 34% over this period, falling from 400 to 260 maternal deaths per 100,000 live births. Between 1990 and 2008, the majority of the global burden of maternal deaths shifted from Asia to Sub-Saharan Africa. Differential trends in fertility, the HIV/AIDS epidemic and access to reproductive health are associated with the shift in the burden of maternal deaths from Asia to Sub-Saharan Africa. CONCLUSIONS Although the estimated annual rate of decline in the global MMR in 1990-2008 (2.3%) fell short of the level needed to meet the MDG 5 target, it was much faster than had been thought previously. Targeted efforts to improve access to quality maternal health care, as well as efforts to decrease unintended pregnancies through family planning, are necessary to further reduce the global burden of maternal mortality.

A Decomposition Method Based on a Model of Continuous Change

A demographic measure is often expressed as a deterministic or stochastic function of multiple variables (covariates), and a general problem (the decomposition problem) is to assess contributions of individual covariates to a difference in the demographic measure (dependent variable) between two populations. We propose a method of decomposition analysis based on an assumption that covariates change continuously along an actual or hypothetical dimension. This assumption leads to a general model that logically justifies the additivity of covariate effects and the elimination of interaction terms, even if the dependent variable itself is a nonadditive function. A comparison with earlier methods illustrates other practical advantages of the method: in addition to an absence of residuals or interaction terms, the method can easily handle a large number of covariates and does not require a logically meaningful ordering of covariates. Two empirical examples show that the method can be applied flexibly to a wide variety of decomposition problems. This study also suggests that when data are available at multiple time points over a long interval, it is more accurate to compute an aggregated decomposition based on multiple subintervals than to compute a single decomposition for the entire study period.

A flexible two-dimensional mortality model for use in indirect estimation

Mortality estimates for many populations are derived using model life tables, which describe typical age patterns of human mortality. We propose a new system of model life tables as a means of improving the quality and transparency of such estimates. A flexible two-dimensional model was fitted to a collection of life tables from the Human Mortality Database. The model can be used to estimate full life tables given one or two pieces of information: child mortality only, or child and adult mortality. Using life tables from a variety of sources, we have compared the performance of new and old methods. The new model outperforms the Coale–Demeny and UN model life tables. Estimation errors are similar to those produced by the modified Brass logit procedure. The proposed model is better suited to the practical needs of mortality estimation, since both input parameters are continuous yet the second one is optional.

The lifetime risk of maternal mortality: concept and measurement

OBJECTIVE The lifetime risk of maternal mortality, which describes the cumulative loss of life due to maternal deaths over the female life course, is an important summary measure of population health. However, despite its interpretive appeal, the lifetime risk of dying from maternal causes can be defined and calculated in various ways. A clear and concise discussion of both its underlying concept and methods of measurement is badly needed. METHODS I define and compare a variety of procedures for calculating the lifetime risk of maternal mortality. I use detailed survey data from Bangladesh in 2001 to illustrate these calculations and compare the properties of the various risk measures. Using official UN estimates of maternal mortality for 2005, I document the differences in lifetime risk derived with the various measures. FINDINGS Taking sub-Saharan Africa as an example, the range of estimates for the 2005 lifetime risk extends from 3.41% to 5.76%, or from 1 in 29 to 1 in 17. The highest value resulted from the method used for producing official UN estimates for the year 2000. The measure recommended here has an intermediate value of 4.47%, or 1 in 22. CONCLUSION There are strong reasons to consider the calculation method proposed here more accurate and appropriate than earlier procedures. Accordingly, it was adopted for use in producing the 2005 UN estimates of the lifetime risk of maternal mortality. By comparison, the method used for the 2000 UN estimates appears to overestimate this important measure of population health by around 20%.