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In medicine, a stent is an artificial tube inserted into a vessel or duct to keep the passageway open. Often it is used to treat narrow or weak arteries.


In clinical trials, stratification is the separation of patients or the analysis of results based on something other than the treatment given.

Stratification has two different meanings. In its first meaning, it describes the natural distribution of patients into subgroups. For instance, patients may be stratified by age, disease severity, or biomarkers.

In its second meaning, stratification controls the random allocation of people to the different groups in a trial. Stratified randomisation is used to ensure that equal numbers of participants with a characteristic thought to affect response to the intervention will be allocated to each group in the trial.

Stratified medicine

Stratified medicine is based on the identification of subgroups of patients that differ in their mechanisms of disease, their susceptibility to a particular disease, or in their response to a medicine. The aim of stratified medicine is to offer the treatment that is most likely to give benefit, or to avoid an adverse reaction. Personalised medicine takes this approach a step further by using targeted medicines and also taking information such as the patient's genotype and lifestyle into account when deciding on the best treatment.

Study medication

The study medication comprises the medicinal product(s) being given to participants in a trial (including a placebo). This also includes products already with a marketing authorisation but being used, formulated, or packaged in a new way, or being used to treat a new disease.

Study Population

The study population is the group of individuals in a study. In a clinical trial, the inclusion and exclusion criteria describe who will and will not be included, thus defining the characteristics of the study population.


This is the administration of a medicine into the layer of skin directly below the dermis and epidermis (the top layers of skin). Subcutaneous tissue has few blood vessels and so medicines administered here are for slow, sustained rates of absorption. An example is a local anaesthetic injected before suturing.


A route of medicine administration in which the medicine is placed under the tongue. These medications can come in the form of tablets, films, or sprays. It is an extremely fast pharmacological route of absorption, as medicines diffuse rapidly into the blood through tissues under the tongue. This is especially effective in an emergency when the medication needs to work immediately like during a heart attack. Another advantage is that the medicine does not go through the digestive system, so it is not metabolised through the liver, and thus a lower dose can be used.


In order to market a medicine, a submission (an application) must be made to the relevant regulatory authority, for example the European Medicines Agency (EMA). Submissions provide comprehensive information about the medicine, its formulation, the trials it has undergone, its intended use, and its risks and benefits.


Subpopulations are groups within a population. The population might be defined by, for example, the presence of a certain disease of interest to researchers. A subpopulation within that will have additional traits, such as disease severity, or failure of previous treatments, or specific genetic traits, or belonging to a certain age group that are also of interest. Subpopulations are identified in this way to allow statistical analysis with respect to the additional traits of interest.

Subunit vaccine

A vaccine derived from physical separation of the antigen from the pathogen.

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