Читать книгу Principles of Virology, Volume 2 - Jane Flint, S. Jane Flint - Страница 36

Although infections of natural populations differ from those under controlled conditions in the laboratory, it is possible to determine if one or more variables affect disease incidence and viral transmission in nature. Two general experimental approaches are used: prospective (also called cohort or longitudinal) and retrospective (or case-controlled) studies. In prospective studies, a population is randomly divided into two groups (cohorts). One group then gets the “treatment of interest,” such as a vaccine or a drug, and the other does not. The negative-control population often receives a placebo. Whether a person belongs to the treatment or placebo cohort is not known to either the recipient or the investigator until the data are collected and the code is broken (“double blind”). This strategy removes potential investigator bias and patient expectations that may otherwise influence data collection. Prospective studies require a large number of subjects, who often are followed for months or years. The number of subjects and time required depend on the incidence of the disease or side effect under consideration and the statistical power, the probability of detecting a difference that is sufficiently significant to draw conclusions.