another [Wellcome Trust Case Control Consortium 2007]. When studies contain related subjects, methods that implicitly assume independence of subjects may have inflated false-positive rates. False negative results may be increased by failure to control various experimental factors, leading to `noise’ in the system and thereby reducing power. Such factors include low quality DNA samples, poorly-performing SNP assays, and errors in sample identification. All of these problems are best handled by appropriate experimental design and quality control, but quality assurance also plays an important role in identifying biases that may be reduced or eliminated during the analysis phase of GWAS.
