A5009660168- Pregnancy and preeclampsia studies
- Birth, Development, and Health
- Ovarian function and disorders
- Statistical Methods and Bayesian Inference
- Advanced Causal Inference Techniques
- Statistical Methods in Clinical Trials
- Statistical Methods and Inference
- Reproductive Health and Contraception
- Reproductive System and Pregnancy
- Endometriosis Research and Treatment
- Assisted Reproductive Technology and Twin Pregnancy
- Pregnancy and Medication Impact
- Effects and risks of endocrine disrupting chemicals
- Gestational Diabetes Research and Management
- Maternal and fetal healthcare
- Reproductive Health and Technologies
- Reproductive Biology and Fertility
- Menstrual Health and Disorders
- Toxic Organic Pollutants Impact
- Health Systems, Economic Evaluations, Quality of Life
- Epigenetics and DNA Methylation
- Nutritional Studies and Diet
- Obesity, Physical Activity, Diet
- Health, Environment, Cognitive Aging
- Maternal and Perinatal Health Interventions
University of Pennsylvania
2021-2025
Eunice Kennedy Shriver National Institute of Child Health and Human Development
2013-2024
California University of Pennsylvania
2022-2024
Johns Hopkins University
2020-2024
University of Michigan
2023
National Institutes of Health
2012-2021
Yale University
2021
McGill University
2021
University of North Carolina at Chapel Hill
2021
University at Buffalo, State University of New York
2002-2020
Overadjustment is defined inconsistently. This term meant to describe control (eg, by regression adjustment, stratification, or restriction) for a variable that either increases net bias decreases precision without affecting bias. We define overadjustment as an intermediate (or descending proxy variable) on causal path from exposure outcome. unnecessary adjustment does not affect of the relation between and outcome but may its precision. use diagrams empirical example (the effect maternal...
The use of biomarkers is ever-increasing importance in clinical diagnosis disease. In practice, a cutpoint required for dichotomizing naturally continuous biomarker levels to distinguish persons at risk disease from those who are not. Two methods commonly used establishing the "optimal" point on receiver operating characteristic curve closest (0,1) and Youden index, J. Both have sound intuitive interpretations—the perfect differentiation farthest none, respectively—and generalizable weighted...
Costs can hamper the evaluation of effectiveness new biomarkers. Analysis smaller numbers pooled specimens has been shown to be a useful cost-cutting technique. The Youden index (J), function sensitivity (q) and specificity (p), is commonly used measure overall diagnostic effectiveness. More importantly, J maximum vertical distance or difference between ROC curve diagonal chance line; it occurs at cut-point that optimizes biomarker's differentiating ability when equal weight given...
The receiver operating characteristic (ROC) curve is used to evaluate a biomarker's ability for classifying disease status. Youden Index (J), the maximum potential effectiveness of biomarker, common summary measure ROC curve. In biomarker development, levels may be unquantifiable below limit detection (LOD) and missing from overall dataset. Disregarding these observations negatively bias thus J. Several correction methods have been suggested mean estimation testing; however, little has...
PURPOSE: To develop risk-adjusted multivariable models that included risk factors and coronary calcium scores determined with electron-beam computed tomography (CT) in asymptomatic patients for the prediction of all-cause mortality. MATERIALS AND METHODS: We followed up a cohort 10,377 individuals undergoing cardiac factor evaluation screening CT. Multivariable Cox proportional hazards were developed to predict Risk-adjusted incorporated traditional disease scores. RESULTS: Cardiac such as...
That conditioning on a common effect of exposure and outcome may cause selection, or collider-stratification, bias is not intuitive. We provide two hypothetical examples to convey concepts underlying due collider. In the first example, fever influenza consumption tainted egg-salad sandwich. second case-status genotype an environmental factor. both examples, imparts association between otherwise independent variables; we call this selection bias.
The literature on exposure to lipophilic agents such as polychlorinated biphenyls (PCBs) is conflicting, posing challenges for the interpretation of potential human health risks. Laboratory variation in quantifying PCBs may account some conflicting study results. For example, quantification purposes, blood often used a proxy adipose tissue, which makes it necessary model serum lipids when assessing risks PCBs. Using simulation study, we evaluated four statistical models (unadjusted,...
Low birth weight (LBW) infants have lower infant mortality in groups which LBW is most frequent. For example, 1991, US born to smokers had higher risks of both and than nonsmokers. However, among infants, was for (relative rate = 0.79). There are competing theories regarding this so-called "paradox." One that maternal smoking beneficial infants. The authors use causal diagrams show that, even the absence any effect smoking, an inverse association due stratification on can be found. This...
What is the relationship between body size, physical activity and semen parameters among male partners of couples attempting to become pregnant? Overweight obesity are associated with a higher prevalence low ejaculate volume, sperm concentration total count. Higher BMI impaired parameters, while increasing waist circumference (WC) also in infertile men. Data from Longitudinal Investigation Fertility Environment (LIFE) Study were utilized. The LIFE study population-based prospective cohort...
Principled methods with which to appropriately analyze missing data have long existed; however, broad implementation of these remains challenging. In this and 2 companion papers (Am J Epidemiol. 2018;187(3):576–584 Am 2018;187(3):585–591), we discuss issues pertaining in the epidemiologic literature. We provide details regarding missing-data mechanisms nomenclature encourage conduct principled analyses through a detailed comparison multiple imputation inverse probability weighting. Data from...
Epidemiologic studies are frequently susceptible to missing information. Omitting observations with variables remains a common strategy in epidemiologic studies, yet this simple approach can often severely bias parameter estimates of interest if the values not completely at random. Even when missingness is random, complete-case analysis reduce efficiency estimated parameters, because large amounts available data simply tossed out incomplete observations. Alternative methods for mitigating...
<h3>Importance</h3> Dietary supplements marketed for male fertility commonly contain folic acid and zinc based on limited prior evidence improving semen quality. However, no large-scale trial has examined the efficacy of this therapy quality or live birth. <h3>Objective</h3> To determine effect daily supplementation <h3>Design, Setting, Participants</h3> The Folic Acid Zinc Supplementation Trial was a multicenter randomized clinical trial. Couples (n = 2370; men aged ≥18 years women 18-45...
Rigorous studies carried out by the National Center for Health Statistics show that previously reported increases in maternal mortality rates United States were an artifact of changes surveillance. The pregnancy checkbox, introduced revised 2003 death certificate and implemented states a staggered manner, resulted increased identification deaths rates. This Commentary summarizes findings reports, describes temporal trends current status States, discusses future concerns. Although studies,...
BackgroundNational Vital Statistics System reports show that maternal mortality rates in the United States have nearly doubled, from 17.4 2018 to 32.9 per 100,000 live births 2021. However, these high and rising could reflect issues unrelated obstetrical factors, such as changes medical conditions or surveillance (eg, due introduction of pregnancy checkbox).ObjectiveThis study aimed assess if conditions, surveillance.Study DesignThe was based on all deaths 1999 Maternal were identified using...
Biomarker use in exposure assessment is increasingly common, and consideration of related issues growing importance. Exposure quantification may be compromised when measurement subject to a lower threshold. Statistical modeling such data requires decision regarding the handling readings. Various authors have considered this problem. In context linear regression analysis, Richardson Ciampi (Am J Epidemiol 2003;157:355–63) proposed replacement below threshold by constant equal expectation for...
Random measurement error can attenuate a biomarker's ability to discriminate between diseased and non-diseased populations. A global measure of biomarker effectiveness is the Youden index, maximum difference sensitivity, probability correctly classifying individuals, 1-specificity, incorrectly health individuals. We present an approach for estimating index associated optimal cut-point normally distributed that corrects random error. also provide confidence intervals these corrected estimates...
The cause of preeclampsia remains unclear. Limited data suggest that excess circulating soluble fms-like tyrosine kinase 1 (sFlt-1), which binds placental growth factor (PlGF) and vascular endothelial (VEGF), may have a pathogenic role.
It is common practice in perinatal epidemiology to calculate gestational-age-specific or birth-weight-specific associations between an exposure and a outcome. Gestational age birth weight, for example, might lie on pathway from the This of conditioning potential intermediate has come under critique various reasons. First, if one interested assessing overall effect outcome, it not necessary stratify, indeed, important intermediate. Second, does condition intermediate, try obtain what...
BACKGROUND: Little is known about the aetiology of endometriosis; however, in presence oxidative stress, reactive oxygen species might increase growth and adhesion endometrial cells peritoneal cavity, leading to endometriosis infertility. Within a study investigating persistent organic compounds endometriosis, authors evaluated association between stress endometriosis. METHODS: Women aged 18–40 years who were undergoing laparoscopy contacted participate (n=100); 84 eligible agreed be...