1991 2012c-630 2014k-223 2017h-709 aging biomedicalresearch clinicalmedicine clinicaltrialsastopic cohortstudies costeffectiveness diagnosis diseases ethics factoranalysis finance financing healthaspects healthservicesresearch lifeexpectancy longitudinalstudies medicalcare medicalpolicy medicalstatistics medicine men men'shealth methods organized persiangulfsyndrome persiangulfwar preventive psychologicalaspects publichealth publishing qz140 r research researchdesign review socialaspects statistical statisticsastopic symptomassessment unitedstates veterans wa306v188t2012 wa950