Deoxyribonucleic acid (DNA) was collected from saliva samples using Isohelix swabs. SNP analyses were performed using the Fluidigm BioMark System (AROS, Aarhus, Denmark) and independently replicated using allelic discrimination assays (TaqMan SNP Genotyping Assays, Life Technologies). The genotyping PCR was carried out on a 7900HT Fast Real-Time PCR System (Applied Biosystems) and the resulting fluorescence data was analyzed with Sequence Detection Software (SDS) 2.3 (Applied Biosystems). The SNP selection was guided by the a priori hypothesis that social learning is modulated by tonic DA levels which may encode the precision of beliefs or predictions and serve to weight trial-wise prediction errors (Friston et al., 2012 (link); Iglesias et al., 2013 (link)). We focused on two genes which play central roles for the synthesis and metabolism of DA, respectively: tyrosine hydroxylase (rs3842727), the rate-limiting enzyme for DA synthesis and Catechol-O-Methyltransferase or COMT (rs4680), a key enzyme for DA metabolism in prefrontal cortex, but also the ventral striatum (Matsumoto et al., 2003 (link); Meyer-Lindenberg et al., 2005; Frank et al., 2007 ; Mier et al., 2010 (link)). The SNPs obtained were used in the random effects group analysis as covariates of interest.