Re: "Invited commentary: unexplained health problems after Gulf War service--finding answers to complex questions".

Numerous studies have investigated the health problems reported by veterans of the Persian Gulf War, but important questions remain. Epidemiologic studies have consistently indicated that Gulf War veterans report unexplained symptoms at significantly higher rates than veteran comparison groups but that they have not experienced excess rates of disease-related mortality. Addressing unanswered questions surrounding post-Gulf-War health problems presents a complex challenge for researchers, but not an insurmountable one. Progress in understanding the role of potential etiologic factors can be made using epidemiologic approaches traditionally applied in the absence of individual exposure data, such as comparisons between veteran subgroups with differing illness profiles and deployment histories.