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Dichotomous factor analysis of symptoms reported by UK and US veterans of the 1991 Gulf War.

J Nisenbaum R, Ismail K, Wessley S, Unwin C, Hull L, Reeves WC
Dichotomous factor analysis of symptoms reported by UK and US veterans of the 1991 Gulf War
Population Health Metric 2004; 2:8, 2004 (The complete electronic version of this article is available at http://www.pophealthmetrics.com/content/2/1/8)

Summary

The symptoms of Gulf War illness (GWI) are similar to those of CFS. As with CFS, despite more than a decade of research no specific cause has been found and it remains unclear if GWI is a specific response to a specific exposure or whether the illness is a non-specific response to a variety of hazards. Also as with CFS, some of the confusion in studies searching for specific causes or markers may represent problems defining the condition. Veterans with GWI report central nervous system problems (e.g., cognition, fatigue), respiratory symptoms, peripheral nervous complaints, gastrointestinal disorders, and mixed somatic symptoms. Factor analysis is a statistical technique that can define specific structures to mixed complaints. This study used factor analysis to determine if symptoms reported by Gulf War veterans from the United Kingdom (UK) and United States (US) had the same structure and if they differed from symptoms described by military personnel not deployed to the Gulf war. This study showed soldiers from both countries who were deployed to the Gulf war suffered a similar illness comprised of gastrointestinal, respiratory, and mood/cognition problems. Similar illness occurred in troops who did not participate in the Gulf war (albeit at lower rates and with different specific characteristics, so we believe that this pattern of symptoms is not unique to Gulf war service nor does it represent a unique illness of Gulf war syndrome.

Abstract

Background: Factor analysis is one of the most used statistical techniques to analyze the interrelationships among symptoms reported by Gulf War veterans. The objective of this study was to apply factor analyses to binary symptom data from the UK study of Gulf War illness and the US Air Force study of Gulf War veterans, and to compare the symptom domains derived from the distinct samples.

Methods: UK veterans of the 1991 Gulf War (n = 3,454), individuals deployed to Bosnia on U.N. peacekeeping operations (n = 1,979) and Gulf War-era servicemen (n = 2,577) who were not deployed to the Gulf were surveyed in 1997-1998, and US 1991 Gulf War veterans from four Air Force units (n = 1,163) were surveyed in 1995 to collect health characteristics including symptoms. Each sample was randomly split in half for exploratory and confirmatory dichotomous factor analyses with promax oblique rotation.

Results: Four correlated factors were identified in each of the samples. Three factors (Respiratory, Mood-Cognition, Peripheral Nervous) overlapped considerably across the UK cohorts. The Gastrointestinal/Urogenital factor in the UK Gulf cohort was noticeably different from the Gastrointestinal factor identified from the Bosnia and Era cohorts. Symptoms from Gulf War UK and U.S. cohorts yielded similar Gastrointestinal, Respiratory and Mood-Cognition factors, despite differences in symptom inventories between the two surveys. A Musculoskeletal factor was only elicited from the US Gulf sample.

Conclusion: Findings of this report are consistent with those from other factor analysis studies that identified similar symptom dimensions between Gulf and non-Gulf War veterans, except that the Gastrointestinal factor in Gulf veterans included other symptom types. Correlations among factors raise the question as to whether there is a general illness, even if not unique to Gulf veterans, representing the common pathway underlying the identified factors. Hierarchical factor analysis models may be useful to address this issue.

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