1991 2014k-223 cohortstudies diagnosis disabilityevaluation diseases factoranalysis healthaspects mentallydisabledpersons peoplewithdisabilities persiangulfsyndrome persiangulfwar psychiatricdisabilityevaluation psychologicaltesting psychologicaltests qz140 researchreport review socialsecurity somatoformdisorders statistical unitedstates veterans wm170