Simulating interventions in graphical chain models for longitudinal data

Simulating the outcome of an intervention is a central problem in many fields as this allows decision-makers to quantify the effect of any given strategy and, hence, to evaluate different schemes of actions. Simulation is particularly relevant in very large systems where the statistical model involves many variables that, possibly, interact with each other. In this case one usually has a large number of parameters whose interpretation becomes extremely difficult. Furthermore, in a real system, although one may have a unique target variable, there may be a number of variables which might, and often should, be logically considered predictors of the target outcome and, at the same time, responses of other variables of the system. An intervention taking place on a given variable, therefore, may affect the outcome either directly and indirectly though the way in which it affects other variables within the system. Graphical chain models are particularly helpful in depicting all of the paths through which an intervention may affect the final outcome. Furthermore, they identify all of the relevant conditional distributions and therefore they are particularly useful in driving the simulation process. Focussing on binary variables, we propose a method to simulate the effect of an intervention. Our approach, however, can be easily extended to continuous and mixed responses variables. We apply the proposed methodology to assess the effect that a policy intervention may have on poorer health in early adulthood using prospective data provided by the 1970 British Birth Cohort Study (BCS70).chain graph, conditional approach, Gibbs Sampling, Simulation of interventions, age at motherhood, mental health

Quantifying the effect of interpregnancy maternal weight and smoking status changes on childhood overweight and obesity in a UK population-based cohort

Background: Maternal preconception and pregnancy exposures have been linked to offspring adiposity. We aimed to quantify the effect of changes in maternal weight and smoking status between pregnancies on childhood overweight/obesity (≥ 85th centile) and obesity (≥ 95th centile) rates in second children. Methods: Records for 5612 women were drawn from a population-based cohort of routinely collected antenatal healthcare records (2003–2014) linked to measured child body mass index (BMI) age 4–5 years. We applied the parametric G-formula to estimate the effect of hypothetical changes between pregnancy-1 and pregnancy-2 compared to the natural course scenario (without change) on child-2 BMI. Results: Observed overweight/obesity and obesity in child-2 at age 4–5 years were 22.2% and 8·5%, respectively. We estimated that if all mothers started pregnancy-2 with BMI 18·5–24·9 kg/m² and all smokers stopped smoking, then child-2 overweight/obesity and obesity natural course estimates of 22.3% (95% CI 21.2–23.5) and 8·3% (7·6–9·1), would be reduced to 18.5% (17.4–19.9) and 6.2% (5.5–7.0), respectively. For mothers who started pregnancy-1 with BMI 18·5–24·9 kg/m², if all smokers stopped smoking, child-2 overweight/obesity and obesity natural course estimates of 17.3% (16.0–18.6) and 5·9% (5·0–6·7) would be reduced to 16.0% (14.6–17.3) and 4·9% (4·1–5·7), respectively. For mothers who started pregnancy-1 with BMI ≥30 kg/m², if BMI was 18·5–24·9 kg/m² prior to pregnancy-2, child-2 overweight/obesity and obesity natural course estimates of 38.6% (34.7–42.3) and 17·7% (15·1–20·9) would be reduced to 31.3% (23.8–40.0) and 12.5 (8.3–17.4), respectively. If BMI was 25.0–29.9 kg/m² prior to pregnancy-2, these estimates would be 34.5% (29.4–40.4) and 14.6% (11.2–17.8), respectively. Conclusion: Interventions supporting women to lose/maintain weight and quit smoking between pregnancies could help reduce rates of overweight/obesity and obesity in second children. The most effective interventions may vary by maternal BMI prior to the first pregnancy

BMI and breast cancer risk around age at menopause

BACKGROUND: A high body mass index (BMI, kg/m 2) is associated with decreased risk of breast cancer before menopause, but increased risk after menopause. Exactly when this reversal occurs in relation to menopause is unclear. Locating that change point could provide insight into the role of adiposity in breast cancer etiology. METHODS: We examined the association between BMI and breast cancer risk in the Premenopausal Breast Cancer Collaborative Group, from age 45 up to breast cancer diagnosis, loss to follow-up, death, or age 55, whichever came first. Analyses included 609,880 women in 16 prospective studies, including 9956 who developed breast cancer before age 55. We fitted three BMI hazard ratio (HR) models over age-time: constant, linear, or nonlinear (via splines), applying piecewise exponential additive mixed models, with age as the primary time scale. We divided person-time into four strata: premenopause; postmenopause due to natural menopause; postmenopause because of interventional loss of ovarian function (bilateral oophorectomy (BO) or chemotherapy); postmenopause due to hysterectomy without BO. Sensitivity analyses included stratifying by BMI in young adulthood, or excluding women using menopausal hormone therapy. RESULTS: The constant BMI HR model provided the best fit for all four menopausal status groups. Under this model, the estimated association between a five-unit increment in BMI and breast cancer risk was HR=0.87 (95% CI: 0.85, 0.89) before menopause, HR=1.00 (95% CI: 0.96, 1.04) after natural menopause, HR=0.99 (95% CI: 0.93, 1.05) after interventional loss of ovarian function, and HR=0.88 (95% CI: 0.76, 1.02) after hysterectomy without BO. CONCLUSION: The BMI breast cancer HRs remained less than or near one during the 45-55 year age range indicating that the transition to a positive association between BMI and risk occurs after age 55

Antecedents and outcomes of young fatherhood: longitudinal evidence from the 1970 British Birth Cohort Study

This paper uses data from the 1970 British Birth Cohort Study to examine who becomes a young father and the circumstances of teenage and younger fathers when they are age 30. Using a life course perspective the paper examines the extent to which younger fathers are more likely to be non-resident and whether early fatherhood and non-residential fatherhood are part of the same developmental pathway. The work explores the factors associated with differential levels of contact and payment of maintenance. Contact and maintenance are affected by the subsequent family formation experiences of the father and the natural mother of the child

The Recuperation of Fertility at Older Ages in Britain: Evidence from the 1958 British Birth Cohort

This paper investigates the factors associated with the postponement and recuperation of childbearing in Britain. First, the paper uses aggregate data from vital registration statistics to examine trends in the timing and quantum of fertility among British birth cohorts from 1940 to 1963. Then, the paper investigates, at the individual level, the demographic and socio-economic factors associated with recuperation among one specific birth cohort. Patterns of childbearing in Britain have changed dramatically over the past 50 years, including an increase in the average age at entry into motherhood, increases in childbearing rates at older ages and an increase in childlessness (Kneale and Joshi, 2008; Sigle Rushton, 2008). However, most recent estimates of cohort fertility suggest that the postponement of fertility may have stabalized, with the 1980 birth cohort experiencing higher fertility rates in their late twenties than was the case for those born in 1975 (ONS, 2009). Fertility patterns in Britain are characterised by large educational differences in the timing of entry into childbearing (Rendall and Smallwood, 2003) and the percentage remaining childless (Berrington, 2004). In this paper we investigate these educational differences for women born in Britain in one week of March 1958 who have been followed up since birth within the National Child Development Study (NCDS). The NCDS is unique in that it provides information on the respondent’s fertility intentions recorded at ages 23, 33 and 42 with observed fertility through to age 50. At each sweep of the study a wealth of other demographic and socio-economic information (such as partnership and employment status) is available. Hence we can extend previous work (Berrington, 2004) examining, in a prospective framework, the relationship between fertility intentions and childbearing outcomes between ages 23 and 33, ages 33 and 42 and ages 42 and 46

The Recuperation of Fertility at Older Ages in Britain: Evidence from the 1958 British Birth Cohort

This paper investigates the factors associated with the postponement and recuperation of childbearing in Britain. First, the paper uses aggregate data from vital registration statistics to examine trends in the timing and quantum of fertility among British birth cohorts from 1940 to 1963. Then, the paper investigates, at the individual level, the demographic and socio-economic factors associated with recuperation among one specific birth cohort. Patterns of childbearing in Britain have changed dramatically over the past 50 years, including an increase in the average age at entry into motherhood, increases in childbearing rates at older ages and an increase in childlessness (Kneale and Joshi, 2008; Sigle Rushton, 2008). However, most recent estimates of cohort fertility suggest that the postponement of fertility may have stabalized, with the 1980 birth cohort experiencing higher fertility rates in their late twenties than was the case for those born in 1975 (ONS, 2009). Fertility patterns in Britain are characterised by large educational differences in the timing of entry into childbearing (Rendall and Smallwood, 2003) and the percentage remaining childless (Berrington, 2004). In this paper we investigate these educational differences for women born in Britain in one week of March 1958 who have been followed up since birth within the National Child Development Study (NCDS). The NCDS is unique in that it provides information on the respondent’s fertility intentions recorded at ages 23, 33 and 42 with observed fertility through to age 50. At each sweep of the study a wealth of other demographic and socio-economic information (such as partnership and employment status) is available. Hence we can extend previous wor

The Impact of Women's Relative Earnings and Gender Equity on the Recuperation of Fertility among Older Couples in Britain

Around one in five women in Britain currently reaching the end of their childbearing years remains childless. Whilst much previous research has highlighted the risk factors for early childbearing, relative little is known in Britain about the factors associated with the successful recuperation of fertility at later ages. This paper uses a couple approach to investigate how entry into parenthood at later ages depends on the man’s and woman’s relative resources and gender role equity. We focus on men and women in their thirties since it is at this age that we see significant recuperation of childbearing in Britain following postponement. The research uses detailed life course data from the 1970 Birth Cohort Study. Childless couples interviewed at age 30 are followed up at ages 34 and 38. At age 30, information was collected about the individual and their partner’s levels of education, employment circumstances, occupation and levels of pay. In addition, the respondent provided data on the division of domestic tasks within the household, their own gender role orientation and their intentions for having children. We use event history analysis to model the timing of first birth as a function of these fixed and time-varying factors. Hence we are able to identify factors associated with the recuperation of fertility and the relative importance of individual and couple level characteristics. We control for the selection into our sample of high-resource couples who remain without a child at age 30. We add to the existing literature in a number of ways: 1) by incorporating recent debates concerning the importance of gender equity on fertility into a broader couple-focused approach, 2) by comparing the fertility outcomes for both men and women and 3) by taking into account a detailed set of fixed and time-varying socio-economic determinants and anticipatory factors

The Recuperation of Fertility at Older Ages in Britain: Evidence from the 1958 British Birth Cohort

This paper investigates the factors associated with the postponement and recuperation of childbearing in Britain. First, the paper uses aggregate data from vital registration statistics to examine trends in the timing and quantum of fertility among British birth cohorts from 1940 to 1963. Then, the paper investigates, at the individual level, the demographic and socio-economic factors associated with recuperation among one specific birth cohort. Patterns of childbearing in Britain have changed dramatically over the past 50 years, including an increase in the average age at entry into motherhood, increases in childbearing rates at older ages and an increase in childlessness (Kneale and Joshi, 2008; Sigle Rushton, 2008). However, most recent estimates of cohort fertility suggest that the postponement of fertility may have stabalized, with the 1980 birth cohort experiencing higher fertility rates in their late twenties than was the case for those born in 1975 (ONS, 2009). Fertility patterns in Britain are characterised by large educational differences in the timing of entry into childbearing (Rendall and Smallwood, 2003) and the percentage remaining childless (Berrington, 2004). In this paper we investigate these educational differences for women born in Britain in one week of March 1958 who have been followed up since birth within the National Child Development Study (NCDS). The NCDS is unique in that it provides information on the respondent’s fertility intentions recorded at ages 23, 33 and 42 with observed fertility through to age 50. At each sweep of the study a wealth of other demographic and socio-economic information (such as partnership and employment status) is available. Hence we can extend previous wor

The Impact of Women's Relative Earnings and Gender Equity on the Recuperation of Fertility among Older Couples in Britain

Around one in five women in Britain currently reaching the end of their childbearing years remains childless. Whilst much previous research has highlighted the risk factors for early childbearing, relative little is known in Britain about the factors associated with the successful recuperation of fertility at later ages. This paper uses a couple approach to investigate how entry into parenthood at later ages depends on the man’s and woman’s relative resources and gender role equity. We focus on men and women in their thirties since it is at this age that we see significant recuperation of childbearing in Britain following postponement. The research uses detailed life course data from the 1970 Birth Cohort Study. Childless couples interviewed at age 30 are followed up at ages 34 and 38. At age 30, information was collected about the individual and their partner’s levels of education, employment circumstances, occupation and levels of pay. In addition, the respondent provided data on the division of domestic tasks within the household, their own gender role orientation and their intentions for having children. We use event history analysis to model the timing of first birth as a function of these fixed and time-varying factors. Hence we are able to identify factors associated with the recuperation of fertility and the relative importance of individual and couple level characteristics. We control for the selection into our sample of high-resource couples who remain without a child at age 30. We add to the existing literature in a number of ways: 1) by incorporating recent debates concerning the importance of gender equity on fertility into a broader couple-focused approach, 2) by comparing the fertility outcomes for both men and women and 3) by taking into account a detailed set of fixed and time-varying socio-economic determinants and anticipatory factors

The Recuperation of Fertility at Older Ages in Britain: Evidence from the 1958 British Birth Cohort

This paper investigates the factors associated with the postponement and recuperation of childbearing in Britain. First, the paper uses aggregate data from vital registration statistics to examine trends in the timing and quantum of fertility among British birth cohorts from 1940 to 1963. Then, the paper investigates, at the individual level, the demographic and socio-economic factors associated with recuperation among one specific birth cohort. Patterns of childbearing in Britain have changed dramatically over the past 50 years, including an increase in the average age at entry into motherhood, increases in childbearing rates at older ages and an increase in childlessness (Kneale and Joshi, 2008; Sigle Rushton, 2008). However, most recent estimates of cohort fertility suggest that the postponement of fertility may have stabalized, with the 1980 birth cohort experiencing higher fertility rates in their late twenties than was the case for those born in 1975 (ONS, 2009). Fertility patterns in Britain are characterised by large educational differences in the timing of entry into childbearing (Rendall and Smallwood, 2003) and the percentage remaining childless (Berrington, 2004). In this paper we investigate these educational differences for women born in Britain in one week of March 1958 who have been followed up since birth within the National Child Development Study (NCDS). The NCDS is unique in that it provides information on the respondent’s fertility intentions recorded at ages 23, 33 and 42 with observed fertility through to age 50. At each sweep of the study a wealth of other demographic and socio-economic information (such as partnership and employment status) is available. Hence we can extend previous work (Berrington, 2004) examining, in a prospective framework, the relationship between fertility intentions and childbearing outcomes between ages 23 and 33, ages 33 and 42 and ages 42 and 46