Twin studies can assess trait modification by genetics or environment by comparing responses to the same treatment within identical twins or by observing if identical and fraternal twins respond similarly to a treatment.

“so there's two ways that you can do studies with twins you either get this twin set and then you do treatment a and b to see response to treatment because they're very similar or the way i like when you want to see trains and how a trait can mode be modified by genetics or environmental factors you get the same set of twin and you give the same drug medication or treatment because then when you look before and after if you don't see if you see that the identical twins they behave in the same way you're going to say well genetics modulating that trait but then if you look at both of them and say they're all over the place they behave in the same way as the identical and the fraternal twins and say well here the environment is playing a big role because genetics is not holding anymore right”