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

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

medical research Medical research (or biomedical research), also known as health research, refers to the process of using scientific methods with the aim to produce knowledge about human diseases, the prevention and treatment of illness, and the promotion of ...

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 at an institution that applies research ethics by reviewing the methods proposed ...

(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 clinical trials and other experiments, as well as observational studies, in medical research involving human beings and involving clinical aspects, including epidemiology . It is the design of experim ...

; 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 ...

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 provide sufficient evidence to reject a particular hypothesis. A statistical hypothesis test typically involves a calculation of a test statistic. T ...

to look for evidence of cause and effect (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 inte ...

; 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 is a set of humans or other organisms in a given region or area. Governments conduct a census to quantify the resident population size within a given jurisdiction. The term is also applied to non-human animals, microorganisms, and pl ...

(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 reason ...

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 ( ) can be roughly defined as a sham medical treatment. Common placebos include inert tablets (like sugar pills), inert injections (like saline), sham surgery, and other procedures. Placebos are used in randomized clinical trials ...

effect,

Hawthorne effect The Hawthorne effect is a type of human behavior 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 Hawthorn ...

, 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