Two paragraphs from the Preface of a book titled "Foundations of Epidemiology":
"Unfortunately, to understand human health, we must study humans—and humans are extremely difficult to study. Unlike laboratory-based sciences, where all conditions are under the control of the scientist, conducting scientific studies with human participants includes a host of complications and potential stumbling blocks. First and foremost, humans do not exist in controlled settings like laboratories. Each person has their own job, their own preferred foods, their own sleep schedule, their own hobbies, their own genetics, their own stress levels, their own set of environmental and social settings—all of which affect health. Since no two people are exactly alike, and since we cannot really tell people what to do, studying them is difficult. Epidemiology is the set of tools we use to study human health. As such, it is not a topic itself per se, but rather a set of research methods that are then applied to other health-related topics (kinesiology, infectious disease, cardiology, child development, etc.). Epidemiology can help answer questions such as the following:
• Are dietary-based or exercise-based interventions better for preventing a second heart attack?
• Which people are at the highest risk of dying from influenza?
• Is it safe to eat raw oysters?
• Do birth control pills cause breast cancer?
• How does Zika virus spread?"
Abstract of a paper titled "Choosing a Method to Reduce Selection Bias: A Tool for Researchers":
"Selection bias is well known to affect surveys and epidemiological studies. There have been numerous methods proposed to reduce its effects, so many that researchers may be unclear which method is most suitable for their study; the wide choice may even deter some researchers, for fear of choosing a sub-optimal approach. We propose a straightforward tool to inform researchers of the most promising methods available to reduce selection bias and to assist the search for an appropriate method given their study design and details. We demonstrate the tool using three examples where selection bias may occur; the tool quickly eliminates inappropriate methods and guides the researcher towards those to consider implementing. If more studies consider selection bias and adopt methods to reduce it, valuable time and resources will be saved, and should lead to more focused research towards disease prevention or cure."
Choosing a Method to Reduce Selection Bias: A Tool for Researchers (Keeble)