You still use theories from psychology to describe the interaction. This is precisely what social-psychology does (admittedly spectacularly often without replic

You still use theories from psychology to describe the interaction. This is precisely what social-psychology does (admittedly spectacularly often without replication). And a good social psychology theory is consistent with other fields of psychology, like cognitive, or—more often—behavioral psychology. You don’t use population statistics to predict how you as an individual will behave in a certain situation.