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Hans-Peter Kohler

Publications and source records attributed to Hans-Peter Kohler.

10 recordsLinked to original sources
PubMed2006

Bio-social determinants of fertility.

This paper reviews several studies that investigated the potential role of genetic factors in determining fertility outcomes. Our review demonstrates convincingly that fertility contains genetic variance; that is, differences between humans in their genetic make-up affects their fertility outcomes and fertility-related behaviours. This finding is robust using both heritabilities and coefficients of genetic variation, and using both direct measures of fertility outcomes and also fertility precursors like fecundity, marriage, fertility expectations and attempts to get pregnant (proception). Moreover, genetic variance can change over short periods of time or across educational levels, specifically for females, and the relevance of genetic variance seems to increase during times of increasing reproductive choice.

Demography↗
PubMed2005

Reformulating and simplifying the DF analysis model.

DeFries-Fulker (DF) Analysis for unselected populations is reformulated as a no-intercept model with centered variables and only two independent variables. The reformulation serves three purposes. First, the original formulation implicitly estimated two different values for c2 and two values for h2. The new formulation resolves this ambiguity. Second, because the original formulation estimated h2 with the coefficient from a regression-interaction term, whether to center the interaction variables was unclear. The new formulation explicitly resolves this issue. Finally, the new formulation estimates fewer parameters, and therefore improves estimation efficiency and statistical power.

Fertility↗
PubMed2005

Social networks, perceptions of risk, and changing attitudes towards HIV/AIDS: new evidence from a longitudinal study using fixed-effects analysis.

The study presented here is an investigation of the importance of social interactions to perceptions of the risk of AIDS, and explores spousal communication about the AIDS epidemic in rural Malawi. A fixed-effects analysis based on longitudinal data collected in 1998 and 2001 shows that social interactions on the subject of HIV/AIDS have significant and substantial effects on respondents' perceptions of the risk of HIV/AIDS, even after controlling for unobserved factors that affect the selection of social networks. These effects are more complex than previously thought. The dominant mechanisms--social learning and social influence--are found to vary by sex and by region, because of regional variations in the marriage pattern and the resulting implications for the formation of local social networks. The conclusion of the study is that rather than fostering denial and inaction, social interactions are an important vector of change in the face of the HIV/AIDS epidemic.

Adult↗
PubMed2004

Patterns of low and lowest-low fertility in Europe.

In this paper we conduct descriptive aggregate analyses to revisit the relationship of low and lowest-low period fertility to cohort fertility and key fertility-related behaviour such as leaving the parental home, marriage, and women's labour force participation. Our analyses show that the cross-country correlations in Europe between total fertility and the total first marriage rate, the proportion of extramarital births, and the labour force participation of women reversed during the period from 1975 to 1999. By the end of the 1990s there was also no longer evidence that divorce levels were negatively associated with fertility levels. We argue that lowest-low fertility has been particularly associated with a 'falling behind' of cohort fertility at higher birth orders and later ages. From these analyses we conclude that the emergence of lowest-low fertility during the 1990s was accompanied by a disruption or even a reversal of many well-known relationships that have been used to explain cross-country differences in fertility patterns.

Adult↗
PubMed2004

Birth month, school graduation, and the timing of births and marriages.

We investigated the timing of fertility and marriage in Sweden using exogenous variation in the age at school graduation that results from differences in birth month. Our analysis found that the difference of 11 months in the age at leaving school between women who were born in two consecutive months, December and January, implies a delay in the age at first birth of 4.9 months. This effect of delayed graduation also persists for the timing of second births and first marriages, but it does not affect completed fertility or the overall probability of marriage before age 45. These results suggest the existence of a relatively rigid sequencing of demographic events in early adulthood, and the age at graduation from school emerges as an important factor in determining the timing--but not the quantum--of familyformation. In addition, these effects point to a potentially important influence of social age, defined by an individual's school cohort, instead of biological age. The relevance of social age is likely due to social interactions and peer-group influences exerted by individuals who are in the same school cohort but are not necessarily of the same age.

Adult↗
PubMed2003

The correlation of fecundability among twins: evidence of a genetic effect on fertility?

BACKGROUND: Numerous rare genetic conditions are known to influence fecundability in both males and females. It is less clear to what extent more subtle genetic differences influence fecundability on a population level. METHODS: In 1994 a population-based survey was conducted among Danish twins born 1953-1982. Fecundability was assessed as the waiting time to pregnancy at the first attempt to achieve a pregnancy. RESULTS: The reported time to pregnancy for males was slightly shorter than for females but there were no sex differences in intrapair similarity. We found an intrapair correlation in time to pregnancy for 645 monozygotic twin pairs (r = 0.22; 95% confidence interval = 0.12 to 0.32), but no intrapair correlation for 826 like-sex dizygotic twin pairs (r = 0.00; 95% confidence interval = -0.09 to 0.10). CONCLUSIONS: The correlation in time to pregnancy for monozygotic twins suggests genetic factors, although similarities in reporting behaviors could also be contributing to the correlation. The lack of correlation in time to pregnancy for dizygotic twins indicates that possible genetic factors of importance for fecundabililty are acting nonadditively. Hence, it may prove difficult to identify specific gene variants that influence fecundability on a population level if their effects depend on gene-gene interactions.

Age Factors↗
PubMed2002

Insulin resistance syndrome: interaction with coagulation and fibrinolysis.

Insulin resistance represents a common metabolic abnormality leading to cardiovascular disease, the major cause of morbidity and mortality in most parts of the world. Insulin resistance is also associated with an increased risk of type 2 diabetes which is strongly associated with obesity. The insulin resistance of obese people and subjects with type 2 diabetes is characterised by defects at many levels, affecting insulin receptor concentration, glucose transport mechanisms and the activities of intracellular enzymes. Around 25% of western populations show some features of the insulin resistance syndrome (often referred to as syndrome X or the metabolic syndrome) ie, a clustering of metabolic, atheromatous risk factors, including hypertriglyceridaemia, hyperinsulinaemia, hyper-tension, hypercholesterinaemia and obesity. However, the known metabolic cardiovascular risk factors associated with the insulin resistance syndrome do not sufficiently explain the excess vascular risk attributed to this syndrome. The observation, that increased plasma plasminogen activator inhibitor 1 (PAI-1) levels were associated with insulin resistance and atherothrombosis added for the first time a pathological basis for an association of the insulin resistance syndrome not only with metabolic, atheromatous (atherosclerotic) risk but also with atherothrombotic risk. It is very likely that not only PAI-1, but also other abnormalities in haemostatic variables contribute to this excess vascular risk. Knowledge of how haemostatic variables cluster with classical metabolic risk factors associated with the insulin resistance syndrome could help to better understand the pathogenesis of cardiovascular diseases. Indeed, many coagulation and fibrinolytic proteins have been shown to be associated with features of the insulin resistance syndrome and these associations suggest that some coagulation and fibrinolytic proteins have a role in atherothrombotic disorders, principally through an association with other established metabolic (atheromatous) risk factors in the presence of underlying insulin resistance. Interestingly, new therapeutic approaches in the prevention and treatment of insulin resistance do show some influence on coagulation and fibrinolysis. The newest drugs are the thiazolidinediones, a totally novel class of insulin sensitisers. They have the potential to offer improvements both in glycaemic control and in cardiovascular events.

Blood Coagulation↗
PubMed2002

Social networks and changes in contraceptive use over time: evidence from a longitudinal study in rural Kenya.

The impacts of social networks on changes in contraception in rural Kenya are investigated using special data from a longitudinal household survey. An analytic model, informed by detailed knowledge of the setting, yielded estimates that indicate that (1) social networks have substantial effects even after unobserved factors (e.g., homophily) that may determine social networks are controlled; (2) controlling for these unobserved factors may substantially alter the estimated effects of networks (these controls were not used in previous studies); (3) network effects are important for both men and women; and (4) network effects are nonlinear and asymmetric, suggesting that networks provide information primarily through social learning, rather than by exerting social influence.

Contraception Behavior↗
PubMedDate not supplied

Between nurture and nature: the shifting determinants of female fertility in Danish twin cohorts.

Behaviors related to fertility constitute primary candidates for investigating the relevance of evolutionary influences and biological dispositions on contemporary human behaviors. Using female Danish twin cohorts born 1870-1968, we document important transformations in the relative contributions of "nurture" and "nature" to within-cohort variations in early and complete fertility, and we point toward a systematic relation between the socioeconomic context of cohorts and the relevance of genetic and shared environmental factors. This transformation is most striking for early fertility where genetic factors strengthen over time and are consistent with up to 50 percent of the variation in early fertility in most recent cohorts. Understanding this emerging relevance of genetic factors is of central importance because early fertility constitutes an important determinant of complete fertility levels in low-fertility societies, and because teenage motherhood and early childbearing are often associated with negative life-cycle consequences. Moreover, our results emphasize the need for socially and contextually informed analyses of nature and nurture that allow both factors to influence human reproductive behavior over time.

Adult↗