Editing Cohort study (section)

==Application==

In medicine, a cohort study is often undertaken to obtain evidence to try to refute the existence of a suspected association between cause and effect; failure to refute a hypothesis often strengthens confidence in it. Crucially, the cohort is identified before the appearance of the disease under investigation. The study groups follow a group of people who do not have the disease for a period of time and see who develops the disease (new incidence). The cohort cannot therefore be defined as a group of people who already have the disease. Prospective (longitudinal) cohort studies between exposure and disease strongly aid in studying causal associations, though distinguishing true causality usually requires further corroboration from further experimental trials.

The advantage of prospective cohort study data is that it can help determine risk factors for contracting a new disease because it is a longitudinal observation of the individual through time, and the collection of data at regular intervals, so recall error is reduced. However, cohort studies are expensive to conduct, are sensitive to [[Attrition (medicine, epidemiology)|attrition]] and take a long follow-up time to generate useful data. Nevertheless, the results that are obtained from long-term cohort studies are of substantially superior quality to those obtained from retrospective/cross-sectional studies. Prospective cohort studies are considered to yield the most reliable results in observational epidemiology. They enable a wide range of exposure-disease associations to be studied.

Some cohort studies track groups of children from their birth, and record a wide range of information (exposures) about them. The value of a cohort study depends on the researchers' capacity to stay in touch with all members of the cohort. Some studies have continued for decades.

In a cohort study, the population under investigation consists of individuals who are at risk of developing a specific disease or health outcome.<ref>{{cite book |editor-first1=Lorna |editor-last1=Fewtrell |editor-first2=Jamie |editor-last2=Bartram |title=Water Quality: Guidelines, Standards, and Health : Assessment of Risk and Risk Management for Water-related Infectious Disease |first1=Ursula J. |last1=Blumenthal |first2=Jay M. |last2=Fleisher |first3=Steve A. |last3=Esrey |first4=Anne |last4=Peasey |chapter=Chapter 7: Epidemiology: a tool for the assessment of risk |publisher=IWA Publishing |year=2001 |chapter-url=https://www.who.int/water_sanitation_health/dwq/iwachap7.pdf |pages=143–144}}</ref>