The simulations presented are not intended to exhaust all the nuances of epistasis, G × E and measurement that might apply in any specific context but they certainly warn investigators not to oversell claims to seek or find G × E for measures of human behavior. Given that human behavioral and psychiatric genetics do not have access to true latent trait values or continuous measures of underlying biological processes, investigators have to rely on scores derived from clusters of indicators such as test items or symptoms. The simulations above confirm the intimate connection between the statistical conclusions drawn about the additive and non-additive contributions of candidate loci and the measured environment to behavioral traits. Even in the simplest case (Table 5) of a two-locus additive model (with no dominance, epistasis or G × E), statistical analysis of counts based on many relatively infrequent symptoms biases results in the direction of detecting substantial epistatic and G × E effects. Indeed, in this simple case, the effects of G × E and epistasis are expected to be more significant than the main
