I presume you have choices for this question? However, I will just discuss on what and why psychologists vary in agreement on validity. Psychologists vary in agreement on the validity of an psychological test. Some would prefer to use concurrent validity or better yet, a criterion validity when it comes to tests. Some might also use construct validity to determine if the construct really measure what it's supposed to measure. Aside from psychological tests, validity would also vary in agreement when it comes to assessments.
