When an informant marks items indicating how often a particular behavior occurs or the severity/intensity of a particular behavior, and how the subject compares with regard to this behavior to others his or her age, the informant is most likely completing a?

The informant is completing a psychological testing through the use of checklist instrument to assess behavior. This develops an understanding and determines certain behaviors using variables which may become a basis for an explanation as it is compared with others. It also gives validity to findings that would be revealed after the tests.