20.3.3 Case Series A case series describes characteristics of a
group of patients with a particular disease or patients who have
undergone a particular procedure. A case series may also involve
observation of larger units such as groups of hospitals or
municipalities, as well as smaller units such as laboratory
samples. Case series may be used to formulate a case definition
of a disease or describe the experience of an individual or
institution in treating a disease or performing a type of
procedure. Case series should comprise consecutive patients or
observations seen by the individual or institution to minimize
selection bias. A case series is not used to test a hypothesis
because there is no comparison group. (Occasionally comparisons
are made with historical controls or published studies, but
these comparisons are informal and should not include formal
statistical analysis.) A report of a case series should include
the rationale for publishing the population description and
inclusion and exclusion criteri