Prospective and retrospective cohorts and case-control studies are some of the most
important study designs in epidemiology because, under certain assumptions, they can …

Confounding is an important source of bias, but it is often misunderstood. We consider how
confounding occurs and how to address confounding using examples. Study results are …

It is common practice in perinatal epidemiology to calculate gestational-age-specific or birth-
weight-specific associations between an exposure and a perinatal outcome. Gestational age …

The epidemiologic study of pregnancy and birth outcomes may be hindered by several
unique and challenging issues. Pregnancy is a time-limited period in which severe cohort …

When investigators describe the study design they employed, the term retrospective cohort
commonly is selected and commonly used incorrectly. In a prospective cohort, investigators …

Abstract Information bias occurs when any information used in a study is either measured or
recorded inaccurately. This paper describes some of the most common types of information …

Preterm delivery is a powerful predictor of newborn morbidity and mortality. Such problems
are due to not only immaturity but also the pathologic factors (such as infection) that cause …

Most reported associations in observational clinical research are false, and the minority of
associations that are true are often exaggerated. This credibility problem has many causes …

The cross-sectional study design is sometimes avoided by researchers or considered an
undesired methodology. Possible reasons include incomplete understanding of the …

Cross‐sectional studies serve many purposes, and the cross‐sectional design is the most
relevant design when assessing the prevalence of disease, attitudes and knowledge among …