Basic Concepts in Epidemiology

Abstract

Basic or core concepts are by no means simple or unimportant. In fact, the true hallmark of an expert is a deeper understanding of basic concepts. In this chapter we will introduce basic epidemiological concepts. Epidemiological research addresses the occurrence of health-relevant characteristics or events in a specified type of people. The characteristic or event of interest is often referred to as the ‘outcome’ and the type of persons in which it occurs is often referred to as the ‘target population’. The frequency of the outcome can be of interest itself, or, the interest may be in the link between the outcome’s frequency and one or more determinants, often called ‘exposures’. Analytical studies address causal links, in contrast to purely descriptive studies. Irrespective of whether a study is descriptive or analytical, empirical evidence is obtained by documenting relevant experiences of a study population, a sampled group of individuals who are intended to represent the target population of interest. To describe such empirical evidence, the frequency concepts of risk, rate, and odds are essential. The frequency of the outcome is often compared among different levels of exposure. In analytical studies, this comparison must strive for freedom from the blurring effects of confounding. In this chapter we explain this phenomenon of confoun­ding. We also discuss the exploration of factors that mediate or modify a causal link. The final section of the chapter discusses types of biases in study findings.

The theory of probabilities is at bottom nothing but common sense reduced to calculus.

Laplace