Candidate gene association studies.

Candidate gene association studies aim to establish or characterise association between the genetic -variation occurring within a specific gene or locus and a phenotype. If the phenotype is quantitative, then the effect size is often measured as the difference between the genotype specific means or a per allele effect. When the phenotype is binary and the disease is either present or absent, the effect is summarised as a genotype specific risk or relative risk. This chapter focuses on methodology employed when a single or small number of genetic loci are being investigated for an association with a specific phenotype.