Despite the exponential growth in the number of papers published in this area in recent years, most measured GxE interaction studies have been limited to a small number of candidate genes, and more specifically, to a small number of purportedly functional polymorphisms in those candidate genes (Belsky et al., 2009). This is in stark contrast to the shift in genetic strategies that has taken place in the field of genetics over a similar time period. Candidate gene studies have largely fallen out of favor in the field of genetics due to recognition that our understanding of the underlying biology of psychological and behavioral outcomes is woefully limited. With falling genotyping costs and rapid developments in technology for high-throughput genotyping (genotyping large numbers of markers at once), gene identification studies have moved toward more atheoretical approaches that allow one to scan the entire genome (so-called genome-wide association studies or GWAS). By using a systematic approach one is not limited to previously known genes of interest. Indeed, in some of the more successful applications of GWAS to complex disorders, such in the
