6. Researchers from the Dunedin Multidisciplinary Study found that the combination of a particular genetic predisposition and stress during adolescence, increases participants' risk for developing depression in adulthood. Critics might question the relevance of the results, given that the kind of stressors experienced by today's youth differ so much from the kinds of stressors experienced by the participants in the 1980s. This is an example of a _________________ effect.