A case series (also known as a clinical series) is a type of

medical research Medical research (or biomedical research), also known as experimental medicine, encompasses a wide array of research, extending from " basic research" (also called ''bench science'' or ''bench research''), – involving fundamental scienti ...

study that tracks subjects with a known exposure, such as patients who have received a similar treatment, or examines their medical records for exposure and outcome. Case series may be ''consecutive'' or ''non-consecutive'', depending on whether all cases presenting to the reporting authors over a period were included, or only a selection. When information on ''more than three patients'' is included, the case series is considered to be a systematic investigation designed to contribute to generalizable knowledge (i.e., ''research''), and therefore submission is required to an

institutional review board An institutional review board (IRB), also known as an independent ethics committee (IEC), ethical review board (ERB), or research ethics board (REB), is a committee that applies research ethics by reviewing the methods proposed for research to ens ...

(IRB). Case series usually contain demographic information about the patient(s), for example, age, gender, ethnic origin. etc. Case series have a descriptive

study design Clinical study design is the formulation of trials and experiments, as well as observational studies in medical, clinical and other types of research (e.g., epidemiological) involving human beings. The goal of a clinical study is to assess the saf ...

; unlike studies that employ an analytic design (e.g.

cohort studies A cohort study is a particular form of longitudinal study that samples a cohort (a group of people who share a defining characteristic, typically those who experienced a common event in a selected period, such as birth or graduation), performing ...

, case-control studies or

randomized controlled trial A randomized controlled trial (or randomized control trial; RCT) is a form of scientific experiment used to control factors not under direct experimental control. Examples of RCTs are clinical trials that compare the effects of drugs, surgical t ...

s), case series do not, in themselves, involve

hypothesis testing A statistical hypothesis test is a method of statistical inference used to decide whether the data at hand sufficiently support a particular hypothesis. Hypothesis testing allows us to make probabilistic statements about population parameters. ...

to look for evidence of

cause and effect Causality (also referred to as causation, or cause and effect) is influence by which one event, process, state, or object (''a'' ''cause'') contributes to the production of another event, process, state, or object (an ''effect'') where the cau ...

(though case-only analyses are sometimes performed in

genetic epidemiology Genetic epidemiology is the study of the role of genetic factors in determining health and disease in families and in populations, and the interplay of such genetic factors with environmental factors. Genetic epidemiology seeks to derive a statist ...

to investigate the association between an exposure and a

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

). Case series are especially vulnerable to

selection bias Selection bias is the bias introduced by the selection of individuals, groups, or data for analysis in such a way that proper randomization is not achieved, thereby failing to ensure that the sample obtained is representative of the population int ...

; for example, studies that report on a series of patients with a certain illness and/or a suspected linked exposure draw their patients from a particular

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction usi ...

(such as a hospital or clinic) which may not appropriately represent the wider population.

Internal validity Internal validity is the extent to which a piece of evidence supports a claim about cause and effect, within the context of a particular study. It is one of the most important properties of scientific studies and is an important concept in reasoni ...

of case series studies is usually very low, due to the lack of a comparator group exposed to the same array of intervening variables. For example, the effects seen may be wholly or partly due to intervening effects such as the

placebo A placebo ( ) is a substance or treatment which is designed to have no therapeutic value. Common placebos include inert tablets (like sugar pills), inert injections (like Saline (medicine), saline), sham surgery, and other procedures. In general ...

effect,

Hawthorne effect The Hawthorne effect is a type of reactivity in which individuals modify an aspect of their behavior in response to their awareness of being observed. The effect was discovered in the context of research conducted at the Hawthorne Western Electric ...

, Rosenthal effect, time effects, practice effects or the natural history effect. Calculating the difference in effects between two treatment groups assumed to be exposed to a very similar array of such intervening effects allows the effects of these intervening variables to cancel out. Hence only the presence of a comparator group, which is not a feature of case-series studies, will allow a valid estimate of the true treatment effect.

References

External links

Study Design Tutorial
Cornell University College of Veterinary Medicine Clinical research {{Medical-stub

See also

References

External links