John AttiaJohn P.A. IoannidisAmmarin ThakkinstianMark McEvoyRodney J. ScottCosetta MinelliJohn ThompsonClaire Infante-RivardGordon GuyattUniversity of Newcastle, AustraliaUniversity of Ioannina, School of MedicineTufts University School of MedicineMahidol UniversityHunter Area Pathology ServiceUniversity of Newcastle Faculty of Medicine and Health SciencesNational Heart and Lung InstituteUniversity of LeicesterMcGill UniversityMcMaster University, Faculty of Health SciencesRoyal Newcastle Hospital2018-09-132018-09-132009-01-14JAMA - Journal of the American Medical Association. Vol.301, No.2 (2009), 191-19715383598009874842-s2.0-58249089746https://repository.li.mahidol.ac.th/handle/20.500.14594/28214In the first article of this series, we reviewed the basic genetics concepts necessary to understand genetic association studies. In this second article, we enumerate the major issues in judging the validity of these studies, framed as critical appraisal questions. Was the disease phenotype properly defined and accurately recorded by someone blind to the genetic information? Have any potential differences between disease and nondisease groups, particularly ethnicity, been properly addressed? In genetic studies, one potential cause of spurious associations is differences between cases and controls in ethnicity, a situation termed population stratification. Was measurement of the genetic variants unbiased and accurate? Methods for determining DNA sequence variation are not perfect and may have some measurement error. Do the genotype proportions observe Hardy-Weinberg equilibrium? This simple mathematic rule about the distribution of genetic groups may be one way to check for errors in reading DNA information. Have the investigators adjusted their inferences for multiple comparisons? Given the thousands of genetic markers tested in genome-wide association studies, the potential for false-positive and false-negative results is much higher than in traditional medical studies, and it is particularly important to look for replication of results. ©2009 American Medical Association. All rights reserved.Mahidol UniversityMedicineReviewSCOPUS10.1001/jama.2008.946