Human Biodemography: Some challenges and possibilities

This opinion report - in a series on the future of biodemography - focuses on promising areas that I think will be valuable to develop in the future in order to get a better understanding of the determinants of the health and well-being of elderly people. I discuss two major themes: i) the benefits of strengthening the ties between biodemography and medical-clinical disciplines to better understand the link between functioning/diseases/ vulnerability and mortality, ii) the male-female health-survival paradox (i.e., males report better health than females, but encounter higher mortality at all ages), and how this paradox may shed light on fundamental aging processes.ageing processes, determinants, elderly, longitudinal, male/female differences, mortality

The age at first birth and completed fertility reconsidered: findings from a sample of identical twins

In this paper we use new methods and data to reassess the relationship between the age at first birth and completed fertility. In particular we attempt to properly estimate the postponement effect, i.e., the reduction in fertility associated with a delay in childbearing, using a sample of Danish monozygotic twins born 1945--60 to control for unobserved heterogeneity. Within-MZ twin pair estimates of the postponement effect indicate that a one year delay in the first birth reduces completed fertility by about 3% for both males and females. The effect is significantly stronger for older cohorts, and it is stronger for females with a late desired entry into parenthood. Analyses that fail to control for unobservables underestimate this postponement effect between 10--25%, and they underestimate the annual decline of this effect by up to 50%. Moreover, our estimates indicate important changes across cohorts in the relevance of child-preferences and ability characteristics for the age at first birth and the pace and level of subsequent fertility. (AUTHORS)

Being born under adverse economic conditions leads to a higher cardiovascular mortality rate later in life: evidence based on individuals born at different stages of the business cycle

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The Fertility Pattern of Twins and the General Population Compared: Evidence from Danish Cohorts 1945-64

Twin studies provide an important possibility for demographers to analyze patterns of heritability and to estimate structural models with controls for endowments. These possibilities are increasingly used in the context of fertility and related behaviors. A close congruence between the fertility patterns of twins and that of the general population, however, is an essential pre-condition in order to generalize the results of twin-based investigations of fertility and related behaviors to the general population. In this paper we therefore compare the fertility of Danish twins born 1945--64 to the fertility pattern of the general population born during the same period. Our analyses find a very close correspondence between the fertility pattern of twins and of the general population. There exist only few statistically significant differences, and the primary difference pertains to the fact that female twins have a slightly later onset of childbearing than non-twins. There are virtually no relevant differences between the fertility patterns of dizygotic and monozygotic twins.cohort fertility, Denmark, fertility, twin studies

Being Born Under Adverse Economic Conditions Leads to a Higher Cardiovascular Mortality Rate Later in Life: Evidence Based on Individuals Born at Different Stages of the Business Cycle

We connect the recent medical and economic literatures on the long-run effects of early-life conditions, by analyzing the effects of economic conditions on the individual cardiovascular (CV) mortality rate later in life, using individual data records from the Danish Twin Registry covering births since the 1870s and including the cause of death. To capture exogenous variation of conditions early in life we use the state of the business cycle around birth. We find a significant negative effect of economic conditions early in life on the individual CV mortality rate at higher ages. There is no effect on the cancer-specific mortality rate. From variation within and between monozygotic and dizygotic twin pairs born under different conditions we conclude that the fate of an individual is more strongly determined by genetic and household-environmental factors if early-life conditions are poor. Individual-specific qualities come more to fruition if the starting position in life is better.longevity, genetic determinants, health, recession, life expectancy, cardiovascular disease, cancer, lifetimes, fetal programming, cause of death, developmental origins

Exogenous determinants of early-life conditions, and mortality later in life

We analyze causal effects of conditions early in life on the individual mortality rate later in life. Conditions early in life are captured by transitory features of the macro environment around birth, notably the state of the business cycle around birth, but also food price deviations, weather indicators, and demographic indicators. We argue that these features can only affect high-age mortality by way of the individual early-life conditions. Moreover, they are exogenous from the individual point of view, which is a methodological advantage compared to the use of unique characteristics of the newborn individual or his family or household as early-life indicators. We collected national annual time-series data on the above-mentioned indicators, and we combine these to the individual data records from the Danish Twin Registry covering births in 1873-1906. The empirical analyses (mostly based on the estimation of duration models) indicate a significant negative causal effect of economic conditions early in life on individual mortality rates at higher ages. If the national economic performance in the year of birth exceeds its trend value (i.e., if the business cycle is favorable) then the mortality rate later in life is lower. The implied effect on the median lifetime of those who survive until age 35 is about 10 months. A systematic empirical exploration of all macro indicators reveals that economic conditions in the first years after birth also affect mortality rates later in life.

Comparison of academic performance of twins and singletons in adolescence : follow-up study

Objectives To determine whether twins in recent cohorts show similar academic performance in adolescence to singletons and to test the effect of birth weight on academic performance in twins and singletons. Design Follow-up study. Setting Denmark. Participants All twins (n = 3411) and a 5% random sample of singletons (n = 7796) born in Denmark during 1986-8. Main outcome measures Test scores in ninth grade (age 15 or 16), birth weight, gestational age at birth, parents’ age, and parents’ education. Results Ninth grade test scores were normally distributed, with almost identical mean and standard deviations for twins and singletons (8.02 v 8.02 and 1.05 v 1.06) despite the twins weighing on average 908 g (95% confidence interval 886 to 930 g) less than the singletons at birth. Controlling for birth weight, gestational age at birth, age at test, and parents’ age and education confirmed the similarity of test scores for twins and singletons (difference 0.04, 95% confidence interval − 0.03 to 0.10). A significant, positive association between test score and birth weight was observed in both twins and singletons, but the size of the effect was small: 0.06-0.12 standard deviations for every kilogram increase in birth weight. Conclusions Although older cohorts of twins have been found to have lower mean IQ scores than singletons, twins in recent Danish cohorts show similar academic performance in adolescence to that of singletons. Birth weight has a minimal effect on academic performance in recent cohorts; for twins this effect is best judged relative to what is a normal birth weight for twins and not for singletons