<P> 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 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 . </P> <P> 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 . </P> <P> In a cohort study, the population under investigation consists of individuals who are at risk of developing a specific disease or health outcome . </P> <Table> <Tr> <Td> </Td> <Td> This section may require cleanup to meet Wikipedia's quality standards . No cleanup reason has been specified . Please help improve this section if you can . (July 2011) (Learn how and when to remove this template message) </Td> </Tr> </Table>

Was the cohort representative of a defined population