cohort 5 years after the baseline survey, Ang et al. (2006) conducted in-person follow-up examinations of 370 Gulf War veterans who had not met the case definition of CWP at baseline. The goal of the follow-up study was to identify predictors of delayed-onset CWP. Of the 370 veterans, 69 (18.6%) had met the classification criteria for CWP at the follow-up evaluation: 51 in the deployed group and 18 in the nondeployed group. According to a logistic multiple-regression model, CWP was significantly associated with perceived life stress (based on responses to the Brief Life Stress Questionnaire) at the time of the Gulf War, whether military related or not (OR 1.4, 95% CI 1.0-2.0), and with perceived life stress in the 6 months after returning home (OR 1.3, 95% CI 1.0-1.8). CWP also correlated with combat exposure during deployment (OR 1.5, 95% CI 1.1-2.0) although not specifically with deployment to the gulf itself (OR 1.1, 95% CI 0.6-2.0). Symptoms of alcohol use at the 5-year baseline survey were protective for CWP at 10 years (OR 0.2, 95% CI 0.1-0.6, p = 0.0039). The authors used the Expanded Combat Exposure Scale in the baseline survey and reported that for every 5-point increase in combat exposure score, there was a 50% increase in the likelihood that a veteran would develop CWP. Although the study had the advantage of using an in-person evaluation for the medical diagnosis of CWP and had a relatively large population of deployed and nondeployed veterans, there was a possibility of recall bias for life and deployment stressors reported 5 years after the conflict, and only veterans from Iowa were evaluated. Furthermore, only veterans who did not meet the CWP criteria at baseline were considered for the follow-up evaluation; veterans who may have developed CWP during the first 5 years after the conflict were not included in the follow-up examination.

Using data from the Iowa Persian Gulf Study Group (1997), Forman-Hoffman et al. (2007) analyzed information from the structured telephone interview conducted with 1896 deployed veterans and 1799 nondeployed veterans in 1995-1996. CWP was based on the following criteria: the veteran reported having fibromyalgia or fibrositis in the previous 12 months or reported overall body pain that occurred almost every day for at least 3 months during the previous 12 months, and had body pain in the 24 hours before the interview. The deployed veterans reported significantly more symptoms of CWP than did nondeployed veterans (OR 2.03, 95% CI 1.60-2.58); the OR was adjusted for age, sex, race, rank, branch of service, military status, smoking, and current income.

Stimpson et al. (2006) surveyed UK veterans who had served only in the Gulf War (n = 2959), only in Bosnia (n = 2052), or both in the Gulf War and in Bosnia (n = 570), and a comparison era group of veterans who had not been deployed to either the Gulf War or Bosnia (n = 2614) for self-reports of CWP. A mailed questionnaire containing a pain manikin to ascertain the pattern and intensity of pain was sent to 12,592 male and female veterans in 1997; the response rate for the three groups was 60-70%. Data from the shaded manikins were used to determine whether the pain pattern met the ACR definition of CWP. The prevalence of reporting of CWP in the Gulf War deployed group (16.8%) and the Gulf War and Bosnia deployed group (15.8%), but not in the Bosnia only deployed group (7.6%), was significantly higher (p < 0.0001) than that in the era group (8.5%). Veterans who reported pain in one limb were also 30 times more likely to report pain in the symmetrically opposite limb rather than a second limb on the same side of the body; the authors found this suggestive of “systemic pain” rather than pain from an injury. Although the sample was large, the study is limited by a lack of physical examination