Editing Epidemiology (section)

=== Case series ===
Case-series may refer to the qualitative study of the experience of a single patient, or small group of patients with a similar diagnosis, or to a statistical factor with the potential to produce illness with periods when they are unexposed.<ref>{{cite journal |last1=Song |first1=Jae W. |last2=Chung |first2=Kevin C. |date=December 2010 |title=Observational Studies: Cohort and Case-Control Studies |journal=Plastic and Reconstructive Surgery |language=en |volume=126 |issue=6 |pages=2234–2242 |doi=10.1097/PRS.0b013e3181f44abc |pmid=20697313 |pmc=2998589 |issn=0032-1052}}</ref>

The former type of study is purely descriptive and cannot be used to make inferences about the general population of patients with that disease. These types of studies, in which an astute clinician identifies an unusual feature of a disease or a patient's history, may lead to a formulation of a new hypothesis. Using the data from the series, analytic studies could be done to investigate possible causal factors. These can include case-control studies or prospective studies. A case-control study would involve matching comparable controls without the disease to the cases in the series. A prospective study would involve following the case series over time to evaluate the disease's natural history.<ref>{{cite book |last1=Hennekens |first1=Charles H. |author2=Julie E. Buring |year=1987 |title=Epidemiology in Medicine |editor=Mayrent, Sherry L. |publisher=Lippincott, Williams and Wilkins |isbn=978-0-316-35636-7 |url-access=registration |url=https://archive.org/details/epidemiologyinme00henn }}</ref>

The latter type, more formally described as [[self-controlled case-series]] studies, divide individual patient follow-up time into exposed and unexposed periods and use fixed-effects Poisson regression processes to compare the incidence rate of a given outcome between exposed and unexposed periods. This technique has been extensively used in the study of adverse reactions to vaccination and has been shown in some circumstances to provide statistical power comparable to that available in cohort studies.{{citation needed|date=June 2022}}