A case series is a medical research descriptive study that tracks patients with a known exposure given similar treatment or examines their medical records for exposure and outcome. It can be retrospective

Retrospective

Retrospective generally means to take a look back at events that already have taken place. For example, the term is used in medicine, describing a look back at a patient's medical history or lifestyle.-Music:...

 or prospective

Prospective

Prospective literally means "looking forward". It can also refer to an event that is likely or expected to happen in the future. For example, a prospective student is someone who is considering attending a school — typically a high school student who is seriously considering applying to a...

 and usually involves a smaller number of patients than more powerful

Statistical power

The power of a statistical test is the probability that the test will reject the null hypothesis when the null hypothesis is actually false . The power is in general a function of the possible distributions, often determined by a parameter, under the alternative hypothesis...

 case-control studies

Case-control

A case-control study is a type of study design in epidemiology. Case-control studies are used to identify factors that may contribute to a medical condition by comparing subjects who have that condition with patients who do not have the condition but are otherwise similar .Case-control studies are...

 or randomized controlled trials

Randomized controlled trial

A randomized controlled trial is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety and efficacy or effectiveness of healthcare services or health technologies A randomized controlled trial (RCT) is a type of scientific experiment - a form of...

. Case series may be consecutive or non-consecutive, depending on whether all cases presenting to the reporting authors over a period of time were included, or only a selection.

Case series may be confounded

Confounding

In statistics, a confounding variable is an extraneous variable in a statistical model that correlates with both the dependent variable and the independent variable...

 by selection bias

Selection bias

Selection bias is a statistical bias in which there is an error in choosing the individuals or groups to take part in a scientific study. It is sometimes referred to as the selection effect. The term "selection bias" most often refers to the distortion of a statistical analysis, resulting from the...

, which limits statements on the causality

Causality

Causality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....

of correlations observed; for example, physicians who look at patients with a certain illness and a suspected linked exposure will have a selection bias in that they have drawn their patients from a narrow selection (namely their hospital or clinic).

External links

• Study Design Tutorial Cornell University College of Veterinary Medicine