“…Initial multiplicative analyses that tested the two genotypes separately in the same analyses did not reveal any MAOA × 5-HTTLPR interactions on any dependent variables reported below (all p >0.1), suggesting that an additive approach is appropriate. Importantly, all analyses reported below, whether split by 5-HTTLPR , MAOA , or their aggregation, always contained groups with at least 13 participants, which is not unlike other LPP studies in clinical populations [e.g., 15 individuals with generalized anxiety disorder (MacNamara and Hajcak, 2010), 13 individuals with anorexia nervosa (Horndasch et al, 2012), or 10 individuals with the 9R-allele of the dopamine transporter gene who tested positive for cocaine in urine (Moeller et al, 2013)], suggesting that the current study was sufficiently powered. Although study investigators were not blinded to genotype or participant grouping during analysis, they were blinded to genotype during study conduct and data collection [note that complete blinding of all relevant participant groupings would have been impractical (e.g., given the extensive cocaine information collected throughout the study, which was important for guaranteeing validity and quality assurance of the data)].…”