In many applications of instrumental variable (IV) methods, the treatments of interest are intrinsically time-varying and outcomes of interest are failure time outcomes. A common example is Mendelian ...randomization (MR), which uses genetic variants as proposed IVs. In this article, we present a novel application of g-estimation of structural nested cumulative failure models (SNCFTMs), which can accommodate multiple measures of a time-varying treatment when modelling a failure time outcome in an IV analysis.
A SNCFTM models the ratio of two conditional mean counterfactual outcomes at time k under two treatment strategies which differ only at an earlier time m. These models can be extended to accommodate inverse probability of censoring weights, and can be applied to case-control data. We also describe how the g-estimates of the SNCFTM parameters can be used to calculate marginal cumulative risks under nondynamic treatment strategies. We examine the performance of this method using simulated data, and present an application of these models by conducting an MR study of alcohol intake and endometrial cancer using longitudinal observational data from the Nurses' Health Study.
Our simulations found that estimates from SNCFTMs which used an IV approach were similar to those obtained from SNCFTMs which adjusted for confounders, and similar to those obtained from the g-formula approach when the outcome was rare. In our data application, the cumulative risk of endometrial cancer from age 45 to age 72 under the "never drink" strategy (4.0%) was similar to that under the "always ½ drink per day" strategy (4.3%).
SNCFTMs can be used to conduct MR and other IV analyses with time-varying treatments and failure time outcomes.
The causes of early childhood linear growth faltering (known as stunting) in low-income and middle-income countries remain inadequately understood. We aimed to determine if the progressive postnatal ...decline in mean height-for-age Z score (HAZ) in low-income and middle-income countries is driven by relatively slow growth of certain high-risk children versus faltering of the entire population.
Distributions of HAZ (based on WHO growth standards) were analysed in 3-month age intervals from 0 to 36 months of age in 179 Demographic and Health Surveys from 64 low-income and middle-income countries (1993–2015). Mean, standard deviation (SD), fifth percentiles, and 95th percentiles of the HAZ distribution were estimated for each age interval in each survey. Associations between mean HAZ and SD, fifth percentile, and 95th percentile were estimated using multilevel linear models. Stratified analyses were performed in consideration of potential modifiers (world region, national income, sample size, year, or mean HAZ in the 0–3 month age band). We also used Monte Carlo simulations to model the effects of subgroup versus whole-population faltering on the HAZ distribution.
Declines in mean HAZ from birth to 3 years of age were accompanied by declines in both the fifth and 95th percentiles, leading to nearly symmetrical narrowing of the HAZ distributions. Thus, children with relatively low HAZ were not more likely to have faltered than taller same-age peers. Inferences were unchanged in surveys regardless of world region, national income, sample size, year, or mean HAZ in the 0–3 month age band. Simulations showed that the narrowing of the HAZ distribution as mean HAZ declined could not be explained by faltering limited to a growth-restricted subgroup of children.
In low-income and middle-income countries, declines in mean HAZ with age are due to a downward shift in the entire HAZ distribution, revealing that children across the HAZ spectrum experience slower growth compared to the international standard. Efforts to mitigate postnatal linear growth faltering in low-income and middle-income countries should prioritise action on community-level determinants of childhood HAZ trajectories.
Bill & Melinda Gates Foundation.
Background:
Previous research has established that childhood emotional abuse has long-term, negative consequences for adult mental health. Yet, less is known about the ways that social relationship ...and education intersect to shape the link between childhood emotional abuse and mental health in adulthood.
Aim:
The current study aims to examine whether perceived quality of social relationships moderates the association between childhood emotional abuse and adult mental health. Moreover, it assesses how the moderating effect of perceived quality of social relationship differs across levels of education.
Method:
The current study analyzes data from the 2012 Korean General Social Survey, a nationally representative sampling of Korean adults. It uses OLS regression models.
Results:
Childhood emotional abuse is positively associated with depression and psychological distress in adulthood. However, perceived quality of social relationships mitigates the positive association of childhood emotional abuse with depression and psychological distress. Further, this buffering effect of perceived quality of social relationships operates only for individuals with less than or equal to a high school education, but not for individuals with college education or more.
Conclusion:
The results lend support to the resource substitution thesis, suggesting that positive perceptions of social relationship act as a protective factor against childhood emotional abuse for individuals with lower levels of education.
In this randomized trial involving 84,585 participants in Poland, Norway, and Sweden, the risk of colorectal cancer at 10 years was lower among those invited to undergo screening colonoscopy than ...among those assigned to no screening.
Service-learning has been gaining traction in Singapore, with many educational institutions integrating it into their curriculum. In the National Institute of Education (NIE), the Group Endeavours in ...Service-Learning (GESL) is an experiential learning opportunity for all student teachers (STs) to collaborate with the community to address local needs. GESL endeavours to build character, and develop positive values and social-emotional competencies. Hence the purpose of this study is to explore how GESL enhances pre-service teacher education in relation to teacher training. Eleven GESL groups were selected, with 12 members from each group randomly recruited to participate in the focus group interviews. A total of 15 focus group interviews were held. The interview data was transcribed, coded and presented in themes by using Interpretative Phenomenological Analysis. Overall, there seemed to be a greater level of self-awareness and understanding of the community needs. Participants reported getting to know themselves better, in terms of their strengths and weaknesses and how they can contribute to the community. There was also enhancement of collaboration, communication and people-management skills. These findings suggest that GESL may be an effective channel to imbue attributes that NIE has identified as important for teaching professionals.
Although many epidemiologic studies focus on point identification, it is also possible to partially identify causal effects under consistency and the data alone. However, the literature on the ...so-called "assumption-free" bounds has focused on settings with time-fixed exposures. We describe assumption-free bounds for the effects of both static and dynamic sustained interventions. To provide intuition for the width of the bounds, we also discuss a mathematical connection between assumption-free bounds and clone-censor-weight approaches to causal effect estimation. The bounds, which are often wide in practice, can provide important information about the degree to which causal analyses depend on unverifiable assumptions made by investigators.
We aimed to demonstrate the use of jackknife residuals to take advantage of the longitudinal nature of available growth data in assessing potential biologically implausible values and outliers.
...Artificial errors were induced in 5% of length, weight, and head circumference measurements, measured on 1211 participants from the Maternal Vitamin D for Infant Growth (MDIG) trial from birth to 24 months of age. Each child's sex- and age-standardized z-score or raw measurements were regressed as a function of age in child-specific models. Each error responsible for a biologically implausible decrease between a consecutive pair of measurements was identified based on the higher of the two absolute values of jackknife residuals in each pair. In further analyses, outliers were identified as those values beyond fixed cutoffs of the jackknife residuals (e.g., greater than +5 or less than −5 in primary analyses). Kappa, sensitivity, and specificity were calculated over 1000 simulations to assess the ability of the jackknife residual method to detect induced errors and to compare these methods with the use of conditional growth percentiles and conventional cross-sectional methods.
Among the induced errors that resulted in a biologically implausible decrease in measurement between two consecutive values, the jackknife residual method identified the correct value in 84.3%–91.5% of these instances when applied to the sex- and age-standardized z-scores, with kappa values ranging from 0.685 to 0.795. Sensitivity and specificity of the jackknife method were higher than those of the conditional growth percentile method, but specificity was lower than for conventional cross-sectional methods.
Using jackknife residuals provides a simple method to identify biologically implausible values and outliers in longitudinal child growth data sets in which each child contributes at least 4 serial measurements.
In this double-blind, randomized trial in Bangladesh, maternal vitamin D supplementation from midpregnancy until birth or 6 months post partum did not improve fetal or infant growth.
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