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Epidemiology is the study of the distribution of disease in a population and the factors, both risk and protective, that cause this distribution.1 Studying the causes, distribution, risk factors, and treatment of diseases provides the cornerstone for research into explaining the root cause and mechanism of transmission for infectious diseases. This chapter is designed to provide a brief introduction to the core principles of clinical research and epidemiology. Our goal is to present clinicians with an overview of the key terms and concepts found throughout published research, and we hope that this chapter will serve as a useful reference for pediatricians seeking to better understand the fundamentals of infectious diseases epidemiology.

In this chapter, we begin with a discussion of study designs, including the strengths and weaknesses of different types of studies. We then explore important concepts used in studies of diagnostic tests: sensitivity, specificity, positive and negative predictive values, and likelihood ratios. Next, we discuss statistical analysis, such as univariate and multivariate analyses, and explaining terms used to define the magnitude of an association, namely, odds ratios (ORs) and relative risk (RR). Finally, we end the chapter with an examination of relative-risk reduction (RRR), absolute-risk reduction (ARR), and number needed to treat (NNT)—measures used to enumerate the benefits of an intervention. We hope that the information presented in this chapter provides a concise overview of the key concepts of epidemiologic and clinical research in infectious diseases.


Various study designs are utilized in clinical research, and each allows authors to address different questions. Depending on whether an author would like to determine the prevalence of a disease, the natural course of an infection, or the effectiveness of a treatment, for example, will determine which study design the investigator will use. In general, studies can be broken down into two principal types: descriptive and analytic. Descriptive studies include case reports, ecological, and cross-sectional studies, all of which are used primarily to generate hypotheses.2–5 As the name implies, these types of study designs allow investigators to describe the characteristics of a single patient or group of patients with a common disease. However, since these studies do not use a control or comparison group, they are poorly suited to make causal inferences. Instead, they are more useful for characterizing emerging or rare diseases, such as the Zika virus, where little is known about the natural course of disease.

Analytic studies consist in hypothesis testing in nature and are better equipped to assess the relationship between exposure and outcome. These studies include case-control and cohort studies, and provide information about prevalence, incidence, causes, risk factors, and outcomes of disease. Experimental studies test the effects of an intervention and include clinical trials, both randomized and nonrandomized. Randomized clinical trials (RCTs) are often considered the most powerful scientific study designs and are the gold standard for evaluating the efficacy ...

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