We considered the questions of where, when, how, and what to measure with respect to epigenetic change in the etiology of psychopathology. With respect to the question of what, it is clear that simply measuring direct epigenetic modification (e.g., methylation or histone alteration) is inadequate; such changes do not necessarily imply alteration in gene expression—the presumed mechanism by which they act. In this way, studies in this area should both measure epigenetic change as well as relevant gene expression profiles to assure that epigenetic modification has had the expected effect on cell physiology. Similarly, with respect to the question of how to measure epigenetic change, research is needed to produce and validate gold standard measures of epigenetic modification. If and after such gold standards are established, studies in this area would do well to adhere to them in the absence of compelling reasons not to do so. In the interim, however, as is required by many journals in the field, findings should be validated across multiple assays to ensure that they are robust and to minimize misclassification bias.
