Despite the large body of research dedicated in recent years to identifying genetic risk factors for psychiatric disorders, results have been characterized by modest effect sizes and limited replication (e.g., Allen et al., 2008; Risch et al., 2009). For example, in a meta-analytic review of 14 studies capturing over 14,000 participants, Risch and colleagues (2009) failed to confirm the landmark Caspi and colleagues (2003) study identifying an interaction between the serotonin transporter gene (5HTTLPR) and life stress on the risk for depression. Instead, Risch et al. (2009) noted a replication failure among studies subsequent to Caspi et al. (2003); across studies, Risch et al. (2009) found no consistent evidence for either a direct relationship between 5HTTLPR and depression, or an interaction between the gene and life events on the risk for depression. This recent finding underscores the importance of quantitative analyses to evaluate the magnitude of effect sizes across studies. In the present study, we conducted an effect size analysis of the association between the serotonin transporter gene and alcohol dependence.
