- used the same procedure in all his studies which helps with comparison, this provides validity (internal) as everything was consistent
- when Milgram varied the physical presence of the experimenter in other variation, he found it did affect obedience (reliable)
- other research has supported his findings e.g. Sedikides and Jackson, conducted a study at New York Zoo where visitors were asked to not lean on the railings. Obedience declined when the visitors were further from the person making the request (61% when in same room, 7% when in an adjacent room) shows his findings are also shown in a. more natural setting