Shaun has been confronted by his roommate for his drinking behavior. Shaun tends to binge drink several times during the week, passing out in random places throughout the apartment. Shaun defends himself by saying that his roommate also drinks, as do most people their age. Today's researchers would call this:

the false consensus effect.      

Explanation:

False consensus effect: In psychology, the term "false consensus effect" is also denoted as "consensus bias" and is determined as a pervasive 'cognitive bias' related to the social inferences, that an individual tends to see his or her own judgements and behavioral choices as appropriate and comparatively common to the existing conditions or circumstances.

In the question above, the given statement signifies the false consensus effect.

answer; paraphrasing;