It should also be kept in mind, however, that methods of assessing aggression vary across age, such that studies of children tend to rely on ratings by teachers and parents, while studies of adults (and some older adolescents) rely more heavily on self-report methods. The confound between method of assessment and age of the subjects has made it difficult in prior studies and metaanalyses to disentangle age effects on heritability from differences that arise from different methods of assessment. Increasing heritability estimates from child to adulthood could therefore also be explained by different methods of assessment as well (e.g., parental bias may lead to overestimation of shared environmental effects and thus attenuate heritability estimates in childhood).
