8.1 Introduction The two most common types of observational study designs in epidemiology are cohort studies and case–control studies. The objective of both these types of studies is to learn…

18.1 Introduction Generational (cohort) life tables versus current (“cross-sectional”) life tables. A life table is a scheme for expressing mortality over an entire lifetime. To accomplish this, we could in…

7.1 Introduction The term cohort derives from the Latin word cohors, meaning “an enclosure.”a This is an apt description of the cohort method because cohort studies follow the experiences of…

19.1 Introduction Random distribution in time and space Epidemiologists are often called upon to evaluate whether an observed number of cases in a population is greater than expected and whether…

9.1 Introduction Random error and systematic error Effective use of epidemiologic information requires more than knowing the facts. It requires understanding the reasoning behind the methods. A good place to…

1.1 Epidemiology and its uses What is epidemiology? The word epidemiology is based on the Greek roots epi (upon), demos (the people, as in “democracy” and “demography”), and logia (“speaking…

6.1 Introduction Epidemiologic experiments are also called trials. The word trial comes from the Anglo-French root trier, meaning “to try” or “to put something to a test.” Epidemiologic trials put…

12.1 Background Initial detection of outbreaks An outbreak is an epidemic or upsurge of cases in a defined geographic region or easily defined subpopulation. Outbreaks come to the attention of…

15.1 Two types of interaction Types of interaction Epidemiologists speak of two distinct types of interaction: biological interaction and statistical interaction. Although these concepts share the term “interaction,” these are…

4.1 Introduction What is descriptive epidemiology? Descriptive epidemiology is a general term used to refer to a broad array of epidemiologic activities whose primary purpose is to describe disease occurrence…