exposures and various outcomes, which may have produced type I errors (false-positive results). No definitive conclusions can be drawn from these studies.
Cherry and colleagues (2001a,b) found that one of their factors identified by factor analysis, which included dizziness and balance, was associated with pesticide exposure. They studied illnesses and exposure in a population-based sample of all UK veterans deployed to the Persian Gulf. (Study details were described earlier.) One of the seven factors, “neurologic,” clustered 13 symptoms, including problems in buttoning, difficulty in rising from a chair, fainting, feeling too weak to complete tasks, losing balance, difficulty in bringing objects down from above the head, double vision, shortness of breath when walking, unsteadiness when walking, and feeling dizzy (Cherry et al., 2001b). Pesticide handling was significantly related to the neurologic factor in the multivariate regression analysis. No clear dose-response association was found with days of exposure to pesticide handling. Personal use of insect repellent and other pesticide and solvent exposures were not statistically significant associated with the neurologic factor.
Kang and colleagues (2002), in a population-based study of US veterans, found that one of their factors identified by factor analysis, which included dizziness and balance, was associated with solvent exposure. The study was the largest and most representative of US veterans (11,441 deployed and 9476 nondeployed veterans). The factor analysis of 47 symptoms identified six factors, only one of which contained a cluster of symptoms that did not load on any factors in the nondeployed Gulf War veterans. The symptoms in the cluster were: loss of balance-dizziness, speech difficulty, blurred vision, and tremors-shaking. A group of 277 deployed veterans (2.4%) and 43 nondeployed veterans (0.45%) met a case definition subsuming all four symptoms. A nested case-control analysis was performed to determine which of 23 self-reported exposures were more common among Gulf War veterans who met the case definition than among Gulf War veterans who lacked any of the symptoms. Of the nine exposures that were at least three times higher among cases, two were solvent-related: CARC paint (51.2% in cases vs 16.3% in controls) and food contaminated with oil smoke (73.4% in cases vs 20.6% in controls). No pesticide-related exposures were reported three or more times more frequently in cases versus controls. A dose-response relationship was not studied, because of the nature of the dataset regarding self-reported exposure. NB testing was not performed, but is likely to be in the final phase of this study.
Two other less representative US studies using factor analysis did not identify a factor related to dizziness and balance. The CDC study (Fukuda et al., 1998), which attempted to define a chronic multisymptom illness, included only a single question that addressed “dizziness or trouble maintaining balance.” No corresponding dizziness or balance-related factor was extracted in the factor analysis by Knoke and colleagues (2000). Haley’s “syndrome 1” (Haley et al., 1997a) contains one symptom (slurred speech) that could overlap with dizziness and balance problems, but the syndrome consists mainly of attention, reasoning, and memory problems that were grouped in a separate “concentration” cluster in the Cherry study (2001b, see above). Haley’s “syndrome 2” (“confusion-ataxia”) also has several symptoms of balance and coordination problems, but none of the pesticide or solvent exposures was related to this particular syndrome. A separate publication by Haley and colleagues (Roland et al., 2000), using audiovestibular testing, reported on the