Validation of a Research Case Definition of Gulf War Illness in the 1991 US Military Population

Abstract

Background: A case definition of Gulf War illness with 3 primary variants, previously developed by factor analysis of symptoms in a US Navy construction battalion and validated in clinic veterans, identified ill veterans with objective abnormalities of brain function. This study tests prestated hypotheses of its external validity. Methods: A stratified probability sample (n = 8,020), selected from a sampling frame of the 3.5 million Gulf War era US military veterans, completed a computer-assisted telephone interview survey. Application of the prior factor weights to the subjects’ responses generated the case definition. Results: The structural equation model of the case definition fit both random halves of the population sample well (root mean-square error of approximation = 0.015). The overall case definition was 3.87 times (95% confidence interval, 2.61–5.74) more prevalent in the deployed than the deployable nondeployed veterans: 3.33 (1.10–10.10) for syndrome variant 1; 5.11 (2.43–10.75) for variant 2, and 4.25 (2.33–7.74) for variant 3. Functional status on SF-12 was greatly reduced (effect sizes, 1.0–2.0) in veterans meeting the overall and variant case definitions. Conclusions: The factor case definition applies to the full Gulf War veteran population and has good characteristics for research.

Epidemiologic Evidence of Health Effects from Long-Distance Transit of Chemical Weapons Fallout from Bombing Early in the 1991 Persian Gulf War

“…The survey objectives, sampling design, allocation and selection of the sample, questionnaire content, data collection and quality control methods, statistical power, methods for constructing sampling weights, and initial findings were published previously in Neuroepidemiology [15]. Briefly, the database of all personnel who were in the US Armed Forces as of August 2, 1990, maintained by the Defense Manpower Data Center (Seaside, Calif., USA), was stratified by age, sex, race, officer versus enlisted rank, military component (active duty vs. activated Reserve/National Guard or recalled retired), special military occupations (air flight crews, aircraft maintenance, army special forces, or other), deployment versus nondeployed to the Kuwaiti Theater of Operations during the conflict period, and in theater location on 20 January 1991.…”

“…In total, 8,020 Gulf War-era veterans were enrolled and interviewed with questions measuring a broad array of symptoms, wartime exposures and family issues. A sampling weight was constructed for each participant combining a survey design weight (the inverse of the probability of selection into the sample), a nonlocation correction weight derived by a logistic regression analysis to correct for the sample members who could not be located, and a nonparticipation correction weight derived similarly to correct for those who were located but declined to participate [15]. Application of the sampling weights in computing the hypothesis tests removes any selection bias introduced by the unequal selection probabilities and minimizes selection bias from inability to locate or obtain participation from sample nonparticipants, allowing the analytic results to reflect the true population effects.…”

“…Subjects satisfied the Overall Factor case definition if they scored ≥1.5 standard deviations on any of the 6 syndrome factor scales. The factor structure was validated by confirmatory factor analysis with structural equation modeling in 335 primarily US Army veterans attending a Gulf War illness clinic at a Veterans Affairs medical center in Texas [17] and again in random split halves of the 8,020 randomly selected participants in the USMHS [15]. …”

“…[15]. A follow-up question asked approximately how many times they heard these chemical warfare detection devices go off.…”

Methods for Measuring Serum Activity Levels of the 192 Q and R Isoenzymes of Paraoxonase 1 in QR Heterozygous Individuals

“…The study population consisted of 2095 veterans [mean age 46.5 years (range 34 -76); 16% women] selected as a representative sample of the 1991 US military population who participated in the US Military Health Survey (21,22 ). The population had relatively low rates of common conditions such as diabetes (10.3%), heart disease (7.7%), liver disease (2.2%), and obesity (body mass index Ͼ35) (10.5%).…”