for the higher SLE groups). Thus this ExE effect (latent E x SLE) would be erroneously interpreted as GxE (heritability x SLE). Only four of the 12 twin studies reviewed provided estimates in both standardized and unstandardized formats (Table 1). Studies of GxE using inferred measures of genotypic variance should report unstandardized moderated twin results and explicitly differentiate whether GxE is due to differences in the actual variance versus the proportion of total variance attributable to genetic influences.
