There are different means to diagnose types. Personally I use a sort of mix between dichotomous typing and element typing.
More precisely :
Step 1 : Find relevant traits, temperaments and interaction styles (basic and derivative)
Step 2 : Find contradictory manifestations - they usually indicate for auxilliary element - for example : Gulenko says that Introtims have deep interests, and Extrotims have wide. Le Pen is clearly an Extrotim but has this characteristic common to Introtims (dominant aspect of introtimness). So I considered this auxilliary and typed Le Pen EIE. I'm pretty sure this is right because my mother has this Introtim-related characteristic and is herself EIE.
Step 3 : Verify manifestations of elements. For example, elements of functions 1, 2, 7 and 8 have somehow equal strength, but 1 and 2 are more differentiated. A LII likes efficiency (), but has usually a hard time to be efficient himself.