subgroups are less representative of the broader Gulf War veteran population than are population-based studies.
Large population-based studies of Gulf War veterans have been conducted in each of the three major countries participating in the Gulf War coalition (e.g., the United States, Canada, and the United Kingdom). These studies have shown consistent findings, in both the nature of unexplained symptoms and their deleterious impact on functioning. Summary features of these studies appear in Table 2.3, along with those of other epidemiologic studies.
Virtually all epidemiologic studies of Gulf War veterans, regardless of study design, rely on self-reports of both symptoms and exposures. As discussed in Chapter 3, studies based on self-reports have inherent limitations because of potential inaccuracies in recalling past events and difficulty in verifying the reports. Most of the larger epidemiologic studies described here were conducted through mail or telephone surveys, precluding the possibility of clinical examination and diagnosis. Comparison groups were veterans of the same era who were not deployed to the Gulf War. More comprehensive reviews of epidemiologic studies of Gulf War veterans are available elsewhere (CDC, 1999; IOM, 1999a).
The “Iowa study,” a major population-based study of U.S. Gulf War veterans, was a cross-sectional survey of a representative sample of 4,886 military personnel who listed Iowa as their home of record at the time of enlistment (Iowa Persian Gulf Study Group, 1997). The study examined the health of military personnel from all branches of service who either were still serving or had left service. The sample was randomly selected from, and therefore representative of, about 29,000 military personnel. Of the eligible study subjects, 3,695 (76 percent) completed a telephone interview. Study subjects were divided into four groups, two that had been deployed to the Gulf War and two that had not been deployed to the Gulf War. Trained examiners using standardized questions, instruments, and scales interviewed the subjects.9 The two groups of Gulf War military personnel reported roughly twice the prevalence of symptoms suggestive of the following conditions: fibromyalgia, cognitive dysfunction, depression, alcohol abuse, asthma, posttrau-
Sources of questions included the National Health Interview Survey, the Behavioral Risk Factor Surveillance Survey, the National Medical Expenditures Survey, the Primary Care Evaluation of Mental Disorders, the Brief Symptom Inventory, the CAGE questionnaire, the PTSD (Posttraumatic Stress Disorder) Checklist—Military, the Centers for Disease Control and Prevention Chronic Fatigue Syndrome Questionnaire, the Chalder Fatigue Scale, the American Thoracic Society questionnaire, the Sickness Impact Profile, and questions to assess fibromyalgia, sexual functioning, and military exposures.