which research method should be used to gather data on the pathological liars and their spouses

Answer 1

What are your choices?

Answer 2

First you need to determine what question about them you are trying to answer. That would influence the method used to gather your data.

However, if you are dealing with pathological liars, it would not be advisable to use any type of questionnaire to be filled out by these people — unless you have away to compare their answers to actual behavior.

I hope this helps. Thanks for asking.