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KEYWORDS

Epidemiology, meta-analysis, clinical trial, cohort, case-control, bias, confounding, relative risk, odds ratio, sensitivity, specificity, patient-reported outcome measures

AT-A-GLANCE

AT-A-GLANCE

  • Epidemiology is the study of disease in a population.

  • Epidemiologic studies may be analytic (including meta-analyses, clinical trials, and cohort and case-control studies) or descriptive.

  • Most epidemiologic studies measure association; causality is difficult to establish with nonexperimental studies.

  • Bias and confounding are important limitations to be aware of, especially in observational studies.

INTRODUCTION

Epidemiology is the study of disease in the population, and it includes the incidence, prevalence, distribution, cause, and natural history of disease. The study of epidemiology is concerned with the health of populations and helps to inform not only the natural history and treatment of disease but also the public health policy of a disease. Epidemiologic studies are often used to help guide evidence-based practice. Most epidemiologic studies are observational, which means that epidemiologists, in their quest to understand a disease, observe a population and how it is affected by a disease without intervening on the population. On the other hand, in experimental studies, a clinical trialist will determine how an intervention affects an individual’s health by actively exposing individuals in a population to an exposure, such as a drug, of interest.

Understanding a disease includes not only identifying the cellular, genetic, and molecular causes and consequences of the illness but also assessing how the disease affects patients and the population in which they reside. Epidemiology is the basic science underpinning this exploration, and epidemiologic techniques are the foundation for nearly all clinical research. Comprehensive clinical training requires knowledge of both the basic science underlying the pathophysiology of disease as well as the epidemiology and natural history of disease. Because the techniques of an epidemiologist are often the basic science of evidence-based medicine, as a practitioner of dermatology, a good foundation in epidemiologic cutaneous science is as important as understanding the molecular basis of skin disease.

BASIC CONCEPTS

DEFINITIONS

The following are basic terms often used to describe epidemiologic studies.

Clinical trials are interventional studies that include randomized controlled trials (RCTs). These studies are considered experimental studies in that the investigator has a direct influence on the subjects in the study via an intervention and evaluates the effect of the intervention. The experimental environment is tightly controlled, allowing an investigator to determine the efficacy an intervention (ie, the effect of an intervention in an ideal setting). Although these studies provide the highest level of proof of an effect by minimizing bias (ie, internal validity), randomized clinical studies many not generalize well to all members of a population (ie, external validity).

Health services research evaluates how an individual receives health care and interacts with the health care system. These studies can include evaluations of access to care, ...

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