Quality control for genome-wide association studies.

This chapter is a comprehensive review of quality control (QC) methods for SNP-based genotyping panels used in genome-wide association studies. These include QC on individuals for missingness, gender checks, duplicates and cryptic relatedness, population outliers, heterozygosity and inbreeding, and QC on SNPs for missingness, minor allele frequency and Hardy-Weinberg equilibrium. The emphasis is on the reasons behind each QC step and on the use of intelligent approaches rather than arbitrary QC thresholds. Scripts and code for performing these QC steps are available at www.kcl.ac.uk/mmg/gwascode/ .