at entry into the military, and education level at the time of entry into the military were controlled for in three models for each psychiatric diagnosis. Combat exposure unadjusted for C-PTSD was found to be significantly associated with MDD (OR 1.22, 95% CI 1.03-1.44) but it was insignificant when adjusted for C-PTSD (OR 1.10, 95% CI 0.92-1.33). C-PTSD unadjusted for combat exposure was also significantly associated with MDD (OR 3.04, 95% CI 1.48-6.24); however, after adjustment for combat exposure, the OR for the association between C-PTSD and MDD was substantially reduced (OR 2.55, 95% CI 1.16-5.61). The investigators suggest that C-PTSD is a mediator of the relationship between combat exposure and MDD. Although the study design using monozygotic twins eliminates the confounding effects of genetic and shared environmental risk factors in the relationships examined, it remains unclear whether other, unmeasured factors might increase the risk of C-PTSD and other mental disorders.

Ikin et al. (2004) conducted in-person interviews of 1381 Australian Gulf War veterans using the CIDI for psychiatric disorders as part of a cross-sectional survey of all Australian veterans deployed to the Gulf War and 1377 comparison veterans not deployed to the gulf. They found that the prevalence of any psychiatric disorder (first present after the Gulf War) was 30.8% in Gulf War veterans and 21.1% in the comparison group (OR 1.6, 95% CI 1.3-1.9) controlled for service type, rank, age, education, and marital status. Deployed veterans were almost 4 times as likely to meet criteria for PTSD (OR 3.9, 95% CI 2.3-6.5) and also were at increased risk for MDD (OR 1.6, 95% CI 1.3-2.0).

Proctor et al. (1998) selected stratified random samples of two demographically heterogeneous Gulf War cohorts from Fort Devens, Massachusetts (n = 2313) and New Orleans (n = 928) that were being studied longitudinally. The resulting subcohorts (Fort Devens, n = 186; New Orleans, n = 66) were compared to a small comparison population of Germany-deployed veterans from the Maine National Guard (n = 48). This study met the criteria for a primary study in that the in-person CAPS was used for PTSD and the SCID was used for other psychiatric disorders. Data were collected in 1994-1996. The samples were selected to produce equal representation of high and low symptom veterans. After adjustment for oversampling of women, participation bias, and age, sex, and education differences, both gulf-deployed groups had higher symptom prevalence of the items that make up the body-system symptom scores in the SF-36 than the Germany-deployed group. Approximately 5% of the Fort Devens cohort, 7% of the New Orleans cohort, and none of the Germany cohort were diagnosed with current PTSD and those with PTSD scored higher on the Expanded Combat Exposure Scale. Compared with the Germany-deployed group, significant differences were found for both gulf-deployed groups in reporting of frequent periods of anxiety or nervousness: OR 7.1 for the Fort Devens cohort and 5.3 for the New Orleans cohort (95% CI excludes 1.0 for both ORs). Self-reported symptoms of frequent periods of feeling depressed were significant only for the Fort Devens cohort (OR 6.0, 95% CI excludes 1.0).

Using the same well-characterized Fort Devens, New Orleans, and Germany-deployed subcohorts as Proctor et al., Wolfe et al. (1999) used the SCID to examine the relationship of psychiatric disorders to health problems. The prevalences of panic disorder, agoraphobia, social phobia, simple phobia, obsessive-compulsive disorder, GAD, and somatoform disorder did not differ between the gulf-deployed and Germany-deployed cohorts. There were slight but significant differences in the rates of current and lifetime PTSD between each of the gulf-deployed groups (5.4% and 6.5%, respectively, in the Fort Devens group and 7.2% and 8.2% in the New Orleans group) and the Germany-deployed group (no PTSD). The largest differences were seen in MDD: all three groups had 2.5-3 times more lifetime MDD than current MDD, and

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