Gulf War and Health Volume 4: Health Effects of Serving in the Gulf War (2006) / Chapter Skim
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3 Considerations in Identifying and Evaluating the Literature
3 Considerations in Identifying and Evaluating the Literature
Pages 45-54
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From page 45... ...
This section describes the major types of epidemiologic studies considered by the committee. Cohort Studies A cohort study is an epidemiologic study that follows a defined group, or cohort, over a period of time.
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From page 46... ...
cohort study differs from a prospective study in temporal direction; investigators look back to classify past exposures in the cohort and then track the cohort forward to ascertain the rate of disease. Cohort studies can be used to estimate a risk difference or a relative risk, two statistics that measure association between the exposure groups.
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The selection of people for the 2The healthy-worker effect arises when a healthy employed population experiences lower mortality than the general population, which consists of a mix of healthy and unhealthy people. A population with increased external traumatic causes of death (such as Gulf War veterans)
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General Remarks Epidemiologic studies can establish statistical associations between exposure to specific agents or situations (for example, deployment to the Gulf War) and health effects, and associations are generally estimated by using relative risks or odds ratios.
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In the Gulf War literature, the key issue is whether the factors identified by factor analysis are exclusive to deployed veterans vs a comparison population, usually nondeployed veterans. Finding factors peculiar to deployed veterans would imply that they might have a new syndrome with specific symptoms that could indicate biologic plausibility or a common pathophysiology, presumably triggered by an exposure that occurred in the Gulf War Theater.
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There are different statistical techniques (such as principal factor, principal component, iterated principal components, and maximal likelihood factor analyses) to determine how well symptoms load onto a particular factor.
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The committee included studies that would answer the question, What does the literature tell us about the health status of Gulf War veterans? To that end, the committee searched the literature and included descriptive epidemiologic studies of health outcomes in military personnel that served in the Gulf War Theater.
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Information bias results from the manner in which data are collected and can result in measurement errors, imprecise measurement, and misdiagnosis. Those types of errors might be uniform in an entire study population or might affect some parts of the population more than others.
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Chapter 4 discusses the limitations. The issues under discussion include the possibility that study samples do not represent to the entire Gulf War population, low rates of participation in studies, self-reporting of symptoms and exposures, narrowness of studies in assessment of health status, insensitivity of instruments for detecting abnormalities in deployed veterans, and the use of period of investigation that is too brief to detect health outcomes that have long latency, such as cancer.
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1995. Irritable bowel syndrome defined by factor analysis.
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