An outcome measure, endpoint, effect measure or measure of effect is a measure within medical practice or

research Research is "creativity, creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization and analysis of evidence to increase understanding of a topic, characterized by a particular att ...

, (primarily

clinical trial Clinical trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietar ...

s) which is used to assess the effect, both positive and negative, of an intervention or treatment. Measures can often be quantified using effect sizes. Outcomes measures can be patient-reported, or gathered through laboratory tests such as blood work,

urine samples A urine test is any medical test performed on a urine specimen. The analysis of urine is a valuable diagnostic tool because its composition reflects the functioning of many body systems, particularly the kidneys and urinary system, and specimens a ...

etc. or through

medical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally consists of a series of questions about the patient ...

. Outcomes measures should be relevant to the target of the intervention (be it a single person or a target population). Depending on the design of a trial, outcome measures can be either primary outcomes, in which case the trial is designed around finding an adequate study size (through proper randomization and power calculation). Secondary or tertiary outcomes are outcome measures which are added after the design of the study is finalized, for example when data has already been collected. A study can have multiple primary outcome measures. Outcome measures can be divided into clinical endpoints and

surrogate endpoint In clinical trials, a surrogate endpoint (or surrogate marker) is a measure of effect of a specific treatment that may correlate with a ''real'' clinical endpoint but does not necessarily have a guaranteed relationship. The National Institutes of He ...

s where the former is directly related to what the goal of the intervention, and the latter are indirectly related.

Relevance

Outcome measures used in trials should consider relevance to the target of the study. In clinical trials such measures of direct importance for an individual may be survival,

quality of life Quality of life (QOL) is defined by the World Health Organization as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards ...

, morbidity,

suffering Suffering, or pain in a broad sense, may be an experience of unpleasantness or aversion, possibly associated with the perception of harm or threat of harm in an individual. Suffering is the basic element that makes up the negative valence of a ...

functional impairment Disability is the experience of any condition that makes it more difficult for a person to do certain activities or have equitable access within a given society. Disabilities may be cognitive, developmental, intellectual, mental, physical, sen ...

or changes in

symptom Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...

s. Outcome measures can be divided into clinical endpoints which are directly relevant to the target and

s (also called "proxy measures"), which are indirectly related. Death from cardiovascular disease is an example of a clinical endpoint, whereas measurements of

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...

, which is not normally associated with any symptoms, is a surrogate endpoint. Other examples of surrogate endpoints are

blood lipoproteins A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, sur ...

and bone density. Composite measures or combined measures are common in clinical research. The rationale is that combining different outcome measures gives greater statistical power. For example, the composite measure

Killed or Seriously Injured Killed or seriously injured (KSI) is a standard metric for safety policy, particularly in transportation and road safety. History ISO 39001 considers a serious injury as having an impact on the body or on the capacity of an individual. Definition ...

" is often used in studies of road safety. While deaths are easier to count and are an outcome of undisputed importance, they are also much fewer than the number seriously injured; many of the "seriously injured" will not have experienced a major life event. However, composite measures should be used with care, particularly when surrogate endpoints are included. A statistically significant effect of a composite measure can often be explained solely by effects of a surrogate endpoint or a variable that is less relevant. It is also possible that composite measures may mask negative treatment effects of truly important outcomes, such as death or cardiovascular events.

References

{{Medical research studies Clinical medicine Research