Overview of Study Design

Abstract Concepts of study design in infectious disease epidemiology have much in common with those in noninfectious disease epidemiology. However, the presence of the infectious agent, separate from but interacting with the human host population, introduces further complexities. Whether a person becomes infected depends on who else in the population is already infected and infectious. Alternatively it may depend on environmental sources of infection. Sir Ronald Ross (Ross 1916) coined the term “dependent happenings” to describe the characteristic of contagious diseases that the number of people becoming newly infected depends on how many are already infected. The transmission of the infectious agent and dependent happenings produce the special aspects of study designs in infectious diseases.