By comparing the association between a parental variable and a measure of child psychopathology between dyads who are genetically related (mothers: homologous IVF, sperm donation, surrogacy; fathers: homologous IVF, egg donation, surrogacy) and genetically unrelated (mothers: egg and embryo donation; fathers: sperm and embryo donation), this natural experimental design approach can be used to examine whether the magnitude of the association between parent and child is primarily genetically mediated, environmentally mediated, or a combination of the two. For example, when an association is identified between rearing parent depression and child depression among genetically related parent and child dyads, but not between genetically unrelated parent and child dyads, the association is attributable to genetic mediation. When the association between rearing parent and child depression is present among genetically related and genetically unrelated dyads, the association cannot be entirely genetically mediated and environmental mechanisms must be influencing the association. Furthermore, similar to the adoption design described earlier, when significant associations are found among genetically unrelated parent-child dyads (i.e., where passive rGE is absent), the primacy of environmental mechanisms underlying this association is
