American Journal of Epidemiology

BackgroundSynthetic cohorts created by combining two cohorts can be useful when no single data set includes both the exposure and outcome data of interest. We estimate the effects of depression in early adulthood on later-life memory outcome using two nationally representative cohorts separately and in a synthetic sample. MethodsWe used the National Longitudinal Study of Youth 1979 (NLSY; N=5,747) and the Health and Retirement Study (HRS; N=6,846) and a synthetic cohort combining exposure data ...

BackgroundThe long preclinical phase of dementia can bias estimated effects of baseline exposures on dementia incidence. We demonstrate simulations informed by reverse Mendelian randomization (MR) findings to quantify the age-specific magnitude of reverse causation bias in analyses in observational studies of the effects of body mass index (BMI) on dementia. MethodsWe simulated longitudinal trajectories of BMI and dementia risk from ages 45 to 90 years, calibrating to published evidence on age-...

OBJECTIVEUsing two cohorts and synthetic datasets, we estimated effects of prospectively reported alcohol use on memory outcomes across middle age. METHODSData were from National Longitudinal Study of Youth 1979 (NLSY79, n=7540, alcohol reports from ages 18-26), Health and Retirement Study (HRS age 50-56 at enrollment, n=13,090), and a synthetic cohort matching early life exposure information from 3,259 NLSY79 participants to later life memory information from 5,451 HRS participants. Covariate-...

ObjectivesGrowth Mindset and Grit have been proposed as key psychological resources for resilience and adaptation, yet their manifestation and social distribution in later life remain underexplored. This study examines the structure, distribution, and correlates of Growth Mindset and Grit in older adulthood using proxy indicators in the English Longitudinal Study of Ageing (ELSA). MethodsProxy indicators reflecting learning behaviour, personality traits, affect, and beliefs were used to derive ...

COVID-19 has been shown to cause a range of harmful long-term effects on nearly every organ system1-3. These findings are based on retrospective studies comparing COVID-19 patients to patients with similar medical histories and demographics but no COVID-19 diagnosis4-16. However, concerns have emerged that these comparisons may be biased if COVID-19 patients had unrelated health conditions or other factors not recorded in their medical records17-21. Here, using a massive dataset of 14.4 billion ...

BackgroundVaccines can prevent severe disease by preventing infection or by reducing progression among those who become infected. Vaccine effectiveness against progression given infection is often used to quantify this second mechanism, but it conditions on infection, which is itself affected by vaccination. As a result, this estimand lacks a clear causal interpretation and may behave non-intuitively over time. MethodsWe introduce a conceptual framework that models protection against infection ...

BackgroundThe Global Youth Tobacco Survey (GYTS) is widely used to monitor tobacco use among adolescents worldwide. However, inconsistent analytical approaches particularly in handling complex survey designs and predictor selection limit comparability across countries, survey waves, and software platforms. Although much of the GYTS literature relies on proprietary tools such as SAS and SPSS, practical and transparent guidance on implementing reproducible, theory-informed analyses remains limited...

Hybrid controlled trials (HCTs) incorporate real-world data into randomized controlled trials (RCTs) by augmenting the internal control arm with patients receiving the same treatment in routine care. Beyond increasing power, HCTs may improve recruitment by supporting unequal randomization ratios that increase patient access to experimental treatments. However, HCT validity is threatened by bias from unmeasured confounding due to lack of randomization of external controls, leading to outcome non-...

BackgroundRoutinely collected health data are increasingly used to generate real-world evidence for therapeutic decision-making. Yet, stakeholders, including clinicians, pharmaceutical industry representatives, patient advocacy groups, and statisticians, prioritize different aspects of data quality, analysis, and interpretation. Without explicit consideration of these perspectives, analyses risk being fragmented, misaligned with end-user needs, or lacking transparency. MethodsWe developed a sta...

Biological ageing begins before birth, with early-life exposures shaping late-life health. These exposures drive health inequities early, yet specific exposures and the composition of the ageing exposome remain largely undefined. This gap may persist as the field lacks agnostic investigations accounting for non-linearity, interactions and subtle signals. We aimed to identify exposures predictive of epigenetic ageing accumulated during childhood and adolescence and explore the composition of the...

Epigenetic clocks estimate biological age from DNA methylation patterns at CpG sites, providing robust predictions of mortality and morbidity risk. "Blue zones"--regions of exceptional longevity--offer a unique opportunity to investigate how biological aging diverges from chronological age. However, standard clocks are typically trained on large, heterogeneous datasets, reflecting average population trends rather than region-specific dynamics. Using data from the Costa Rican Longevity and Health...

BackgroundSmoking, unhealthy nutrition, alcohol consumption, and physical inactivity (SNAP behaviours) are major risk factors for multimorbidity but are often studied in isolation. Using longitudinal data, Suhag et al. identified clusters of older adults (aged [≥]50) with common SNAP behaviour patterns and distinct sociodemographic profiles and multimorbidity prevalence; whether and how these patterns generalise across adulthood remains unclear. AimTo conceptually replicate Suhag et al. acro...

IntroductionTobacco smoking remains a leading cause of preventable death in the UK. Although e-cigarettes are promoted as a harm-reduction option, longitudinal evidence on short-term health outcomes across different smoking transition pathways is limited. This study examined short-term associations between transitions to exclusive e-cigarette use, dual use, or cessation and physical health, mental health, and health-related quality of life, compared with continued smoking. MethodsA target trial...

BackgroundHelicobacter pylori infection accounts for 98% of gastric cancer (GC) cases in Japan. Since 2013, the nationwide expansion of H. pylori eradication therapy to chronic gastritis patients has created a unique opportunity to evaluate its population-level impact on GC primary prevention. However, short-term reductions in GC deaths are difficult to interpret given the long natural history of gastric carcinogenesis. This study aimed to assess the early impact of population-level eradication ...

The two largest US measles outbreaks in over two decades (2025 Gaines County, Texas: 414 cases, contained; 2025-2026 Spartanburg County, South Carolina: 923+ cases, ongoing) occurred in counties with similar sub-threshold K-12 MMR coverage (85.1% vs 88.8%), yet their trajectories diverged dramatically. Using kernel density estimation with a common bandwidth and bootstrap uncertainty quantification, we compared sub-county vaccination data at the district level for Texas (3 districts, 3,560 studen...

PURPOSEOver 6.9 million Americans above the age of 65 are living with Alzheimers Disease (AD) or related dementias (ADRDs), which are diseases characterized by cognitive decline and structural brain changes associated with accelerated brain aging. Cardiovascular risk factors, in particular hypertension, are well-studied risk factors for AD/ARD. Evidence suggests that the effects of hypertension on cognitive aging may vary by life stage, yet prior studies have focused on the effects of mid- or la...

ObjectiveTo evaluate risk of early-onset dementia (EOD) after diagnosis of cancer among Medicaid beneficiaries. DesignLongitudinal observational study of Medicaid enrollment, inpatient, and outpatient claims data from 26 states and Washington, DC, 2001-2019. MethodsBeneficiaries aged 18-64 with [≥]6 months of enrollment were matched 1:1 on cancer status (lung, colon, breast, prostate) by age, sex, race, year and state. We estimated the weighted cumulative incidence functions of EOD at 1, 2,...

ObjectivesEstimate the HIV testing, diagnoses, and test positivity rates among Medicaid beneficiaries in 2016-2021 and assess the impact of the COVID-19 pandemic on these outcomes. DesignProspective observational study of Medicaid enrollment, inpatient, and outpatient claims data from 27 states, 2016-2021. MethodsWe assessed Medicaid claims from adult beneficiaries with full benefits whose first continuous enrollment was [≥]6 months without dual enrollment in other insurance, and without pr...

Mendelian randomization has emerged as a transformative approach for inferring causal relationships between risk factors and disease outcomes. However, applying Mendelian randomization to disease progression - a critical step in validating pharmacological targets - is hampered by index event bias. This form of selection bias occurs because analyses of disease progression are necessarily restricted to individuals who have already experienced the disease event. Here, we present a comprehensive eva...

Since the cessation of real-time monitoring of COVID-19 hospitalizations in early 2024, the burden of and vaccine effectiveness (VE) against severe COVID-19 in the Netherlands was largely unknown. Recently, hospitalization data from 2024 were made available for the purpose of monitoring and evaluating the COVID-19 vaccination campaigns. These data were linked to the population registry, vaccination registry and healthcare use data (for classification into medical risk groups). We analyzed the n...