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BACKGROUND Evidence suggesting that persistent environmental pollutants may be reproductive toxicants underscores the need for prospective studies of couples for whom exposures are measured. OBJECTIVES We examined the relationship between selected persistent pollutants and couple fecundity as measured by time to pregnancy. METHODS A cohort of 501(More)
STUDY QUESTION What is the relationship between body size, physical activity and semen parameters among male partners of couples attempting to become pregnant? SUMMARY ANSWER Overweight and obesity are associated with a higher prevalence of low ejaculate volume, sperm concentration and total sperm count. WHAT IS KNOWN ALREADY Higher BMI is associated(More)
The relationship between the environment and human fecundity and fertility remains virtually unstudied from a couple-based perspective in which longitudinal exposure data and biospecimens are captured across sensitive windows. In response, we completed the LIFE Study with methodology that intended to empirically evaluate a priori purported methodological(More)
BACKGROUND The relation between persistent environmental chemicals and semen quality is evolving, although limited data exist for men recruited from general populations. OBJECTIVES We examined the relation between perfluorinated chemicals (PFCs) and semen quality among 501 male partners of couples planning pregnancy. METHODS Using population-based(More)
The secondary sex ratio (SSR), defined as the ratio of males to females at birth, has been investigated in relation to endocrine disruptors to search for environmental toxicants perturbing human sex selection. Benzophenone (BP)-type ultraviolet (UV) filters, which are used in sunscreens and personal care products, have been reported to exert estrogenic and(More)
Group key agreement protocols are designed to solve the fundamental problem of securely establishing a session key among a group of parties communicating over a public channel. Although a number of protocols have been proposed to solve this problem over the years, they are not well suited for a high-delay wide area network; their communication overhead is(More)
In this paper, we consider theoretical and computational connections between six popular methods for variable subset selection in generalized linear models (GLM's). Under the conjugate priors developed by Chen and Ibrahim (2003) for the generalized linear model, we obtain closed form analytic relationships between the Bayes factor (posterior model(More)
OBJECTIVE To assess salivary stress biomarkers (cortisol and α-amylase) and female fecundity. DESIGN Prospective cohort design. SETTING United Kingdom. PATIENT(S) 274 women aged 18 to 40 years who were attempting pregnancy. INTERVENTION(S) Observation for six cycles or until pregnancy: women collected basal saliva samples on day 6 of each cycle, and(More)
In a typical case-control study, exposure information is collected at a single time point for the cases and controls. However, case-control studies are often embedded in existing cohort studies containing a wealth of longitudinal exposure history about the participants. Recent medical studies have indicated that incorporating past exposure history, or a(More)
In the analysis of censored survival data Cox proportional hazards model (1972) is extremely popular among the practitioners. However, in many real-life situations the proportionality of the hazard ratios does not seem to be an appropriate assumption. To overcome such a problem, we consider a class of nonproportional hazards models known as generalized(More)