The Formal Demography of Peak Population.

When will the human population peak? In this article, we build on classical results by Ansley Coale, who showed that when fertility declines steadily, births reach their maximum before fertility reaches replacement level, and the decline in total population size does not occur until several decades after fertility has reached that level. We extend Coale's results by modeling longevity increases, net immigration, and a slowdown in fertility decline that resembles current projections. With these extensions, our models predict a typical lag between replacement-level fertility and population decline of about 35 to 40 years, consistent with projections by the United Nations and about 15 years longer than the lag predicted by Coale. Our analysis helps reveal underlying factors in the timing of peak population.

CenSoc: Public Linked Administrative Mortality Records for Individual-level Research.

In the United States, much has been learned about the determinants of longevity from survey data and aggregated tabulations. However, the lack of large-scale, individual-level administrative mortality records has proven to be a barrier to further progress. We introduce the CenSoc datasets, which link the complete-count 1940 U.S. Census to Social Security mortality records. These datasets-CenSoc-DMF (N = 4.7 million) and CenSoc-Numident (N = 7.0 million)-primarily cover deaths among individuals aged 65 and older. The size and richness of CenSoc allows investigators to make new discoveries into geographic, racial, and class-based disparities in old-age mortality in the United States. This article gives an overview of the technical steps taken to construct these datasets, validates them using external aggregate mortality data, and discusses best practices for working with these datasets. The CenSoc datasets are publicly available, enabling new avenues of research into the determinants of mortality disparities in the United States.

Naming the Precious Child: New Evidence of Intentional Family Planning in Historical Populations.

Can the names parents gave their children give us insights into how parents in historical times planned their families? In this study, we explore whether the names given to the firstborn child can be used as indicators of family-size preferences and, if so, what this reveals about the emergence of intentional family planning over the course of the demographic transition. We analyze historical populations from 1850 to 1940 in the United States, where early fertility control and large sample sizes allow separate analyses of the White and Black populations. We also analyze Norway from 1800 to 1910, where there was a much later fertility transition. A split-sample method allows automated scoring of each name in terms of predicted family size. We find a strong relationship between naming and family size in the U.S. White population as early as 1850, for the Black population beginning in 1940, and for the Norwegian population in 1910. These results provide new evidence of the emergence of "conscious calculation" during the fertility transition. Our methods may also be applicable to modern high-fertility populations in the midst of fertility decline.

Examining the population level and individual level longitudinal stability of psychosocial measures in the US Army's Global Assessment Tool (GAT).

As a component of the US Army's Comprehensive Soldier and Family Fitness program (CSF2), the Global Assessment Tool (GAT) represents a multidimensional constellation of measures designed to assess characteristics related to resilience. Using a foundation of validated measures from prior research, the GAT has been the vehicle for self-assessment to provide Soldiers, their families, and Army Civilians snapshots of their psychosocial wellness. Despite the long history of the measurement instrument (first implemented in 2009) and widespread use (mandatory for all active-duty Soldiers annually), the longitudinal capabilities of the GAT has received little attention. Here, we examine the longitudinal stability of the GAT across an approximate five-year time frame and multiple statistical approaches that demonstrate measurement stability at both the aggregate population level (people on average) and the individual level. We find evidence that the majority of the measures within the GAT are relatively stable over time both at the population level and individual level. This evidence contributes to knowledge of how best to improve the GAT for future use with the pay-off for the Army being a self-assessment tool that is more effective and efficient.

Vaccinating the oldest against COVID-19 saves both the most lives and most years of life.

Many competing criteria are under consideration for prioritizing COVID-19 vaccination. Two criteria based on age are demographic: lives saved and years of future life saved. Vaccinating the very old against COVID-19 saves the most lives, but, since older age is accompanied by falling life expectancy, it is widely supposed that these two goals are in conflict. We show this to be mistaken. The age patterns of COVID-19 mortality are such that vaccinating the oldest first saves the most lives and, surprisingly, also maximizes years of remaining life expectancy. We demonstrate this relationship empirically in the United States, Germany, and South Korea and with mathematical analysis of life tables. Our age-risk results, under usual conditions, also apply to health risks.

Demographic perspectives on the mortality of COVID-19 and other epidemics.

To put estimates of COVID-19 mortality into perspective, we estimate age-specific mortality for an epidemic claiming for illustrative purposes 1 million US lives, with results approximately scalable over a broad range of deaths. We calculate the impact on period life expectancy (down 2.94 y) and remaining life years (11.7 y per death). Avoiding 1.75 million deaths or 20.5 trillion person years of life lost would be valued at $10.2 to $17.5 trillion. The age patterns of COVID-19 mortality in other countries are quite similar and increase at rates close to each country's rate for all-cause mortality. The scenario of 1 million COVID-19 deaths is similar in scale to that of the decades-long HIV/AIDS and opioid-overdose epidemics but considerably smaller than that of the Spanish flu of 1918. Unlike HIV/AIDS and opioid epidemics, the COVID-19 deaths are concentrated in a period of months rather than spread out over decades.

The changing relationship between unemployment and total fertility.

The aim of this paper is to investigate whether there has been a fundamental change in the relationship between economic conditions and fertility. We use panel data methods to study the short-term changes in total fertility and the unemployment rate in a range of Organisation for Economic Co-operation and Development (OECD) countries from 1957 to 2014. We find that although fertility was counter-cyclical before 1970, with good economic times being associated with lower fertility, since then it has become pro-cyclical, with good economic times being associated with higher fertility.

From Patrick to John F.: Ethnic Names and Occupational Success in the Last Era of Mass Migration.

Taking advantage of historical census records that include full first and last names, we apply a new approach to measuring the effect of cultural assimilation on economic success for the children of the last great wave of immigrants to the United States. We created a quantitative index of ethnic distinctiveness of first names and show the consequences of ethnic-sounding names for the occupational achievement of the adult children of European migrants. We find a consistent tendency for the children of Irish, Italian, German, and Polish immigrants with more "American"-sounding names to have higher occupational achievement. About one-third of this effect appears to be due to social class differences in name-giving, and the remaining two-thirds to signaling effects of the names themselves. An exception is found for Russian, predominantly Jewish, immigrants, where we find a positive effect of ethnic naming on occupational achievement. The divergent effects of our new measure of cultural assimilation, sometimes hurting and sometimes helping, lend historical empirical support to more recent theories of the advantages of different paths to assimilation. The effects of first names are robust to controls for the ethnic recognizability of last names, suggesting that immigrants' success depended on being perceived as making an effort to assimilate rather than hiding one's origins.

A cohort model of fertility postponement.

We introduce a new formal model in which demographic behavior such as fertility is postponed by differing amounts depending only on cohort membership. The cohort-based model shows the effects of cohort shifts on period fertility measures and provides an accompanying tempo adjustment to determine the period fertility that would have occurred without postponement. Cohort-based postponement spans multiple periods and produces "fertility momentum," with implications for future fertility rates. We illustrate several methods for model estimation and apply the model to fertility in several countries. We also compare the fit of period-based and cohort-based shift models to the recent Dutch fertility surface, showing how cohort- and period-based postponement can occur simultaneously.

Probabilistic forecasting using stochastic diffusion models, with applications to cohort processes of marriage and fertility.

In this article, we show how stochastic diffusion models can be used to forecast demographic cohort processes using the Hernes, Gompertz, and logistic models. Such models have been used deterministically in the past, but both behavioral theory and forecast utility are improved by introducing randomness and uncertainty into the standard differential equations governing population processes. Our approach is to add time-series stochasticity to linearized versions of each process. We derive both Monte Carlo and analytic methods for estimating forecast uncertainty. We apply our methods to several examples of marriage and fertility, extending them to simultaneous forecasting of multiple cohorts and to processes restricted by factors such as declining fecundity.

How slowing senescence translates into longer life expectancy.

Mortality decline has historically been largely a result of reductions in the level of mortality at all ages. A number of leading researchers on ageing, however, suggest that the next revolution of longevity increase will be the result of slowing down the rate of ageing. In this paper, we show mathematically how varying the pace of senescence influences life expectancy. We provide a formula that holds for any baseline hazard function. Our result is analogous to Keyfitz's 'entropy' relationship for changing the level of mortality. Interestingly, the influence of the shape of the baseline schedule on the effect of senescence changes is the complement of that found for level changes. We also provide a generalized formulation that mixes level and slope effects. We illustrate the applicability of these models using recent mortality decline in Japan and the problem of period to cohort translation.

Has East Germany overtaken West Germany? Recent trends in order-specific fertility.

Some 20 years after reunification, the contrast between East and West Germany offers a natural experiment for studying the degree of persistence of Communist-era family patterns, the effects of economic change, and fertility postponement. After reunification, period fertility rates plummeted in the former East Germany to record low levels. Since the mid-1990s, however, period fertility rates have been rising in East Germany, in contrast to the nearly constant rates seen in the West. By 2008, the TFR of East Germany had overtaken that of the West. We explore why fertility in East Germany is higher than in West Germany, despite unfavorable economic circumstances in the East. We address this and related questions by (a) presenting an account of the persisting East/West differences in attitudes toward and constraints on childbearing, (b) conducting an order-specific fertility analysis of recent fertility trends, and (c) projecting completed fertility for the recent East and west German cohorts. In addition to using the Human Fertility Database, perinatal statistics allow us to calculate a tempo-corrected TFR for East and West Germany.

A secular trend toward earlier male sexual maturity: evidence from shifting ages of male young adult mortality.

This paper shows new evidence of a steady long-term decline in age of male sexual maturity since at least the mid-eighteenth century. A method for measuring the timing of male maturity is developed based on the age at which male young adult mortality accelerates. The method is applied to mortality data from Sweden, Denmark, Norway, the United Kingdom, and Italy. The secular trend toward earlier male sexual maturity parallels the trend toward earlier menarche for females, suggesting that common environmental cues influence the speed of both males' and females' sexual maturation.

Relationships between period and cohort life expectancy: gaps and lags.

This paper offers an empirical and analytic foundation for regarding period life expectancy as a lagged indicator of the experience of real cohorts in populations experiencing steady improvement in mortality. We find that current period life expectancy in the industrialized world applies to cohorts born some 40-50 years ago. Lags track an average age at which future years of life are being gained, in a sense that we make precise. Our findings augment Ryder's classic results on period-cohort translation.

Terror attacks influence driving behavior in Israel.

Terror attacks in Israel produce a temporary lull in light accidents followed by a 35% spike in fatal accidents on Israeli roads 3 days after the attack. Our results are based on time-series analysis of Israeli traffic flows, accidents, and terror attacks from January 2001 through June 2002. Whereas prior studies have focused on subjective reports of posttraumatic stress, our study shows a population-level behavioral response to violent terror attacks.

Population momentum for gradual demographic transitions: an alternative approach.

In this article, I derive a simple formula for approximating the ultimate size of a population that undergoes a gradual transition to replacement fertility. I model the fertility transition by specifying a linear frontier on the Lexis surface across which a change in fertility is instantaneous. Gradual transitions result from variations in the slope of this frontier. This framework can be used to reproduce and understand previous studies of population momentum and gradual transitions.