psychologists are fairly big on their tests because it is something distinctive that they do. they develop tests and they are trained to administer tests and they are trained to interpret findings. psychological testing is the domain of the psychologists (and they can be fairly... um... protective about their tests.

this isn't so unusual...

psychiatrists are fairly big on their medications because it is something distinctive that they do. they are trained to administer medications and prescribe them. medication is the domain of the psychiatrists (and they can be fairly... um... protective about their medication). 'cept for the anti-psychiatrists, of course, who are more into their psychoanalysis (thinking of Szasz in particular).

the MMPI test takes your self reported answers as input and delivers a score on a number of dimensions (or traits, i guess). probably best for you not to know what the dimensions / traits are or it will %#@&#! up your score because you will be trying to figure out what dimension each question is scoring you for. some of the questions are delightfully unobvious. there is also a surprising correlation that gives me a kick! but i don't think i should disclose that one... it is something along the lines of (making this up as an example) people with dimension x (anxiety, for example) tending to have an affinity for the colour blue and so if you answer 'blue is my favourite colour' you get a score towards anxiety!

so basically the data will look a bit like:
dimension 1: score
dimension 2: score
dimension 3: score
and so on. i think there might be some fancy math (woo hoo graduate level statistics is useful for something!!!!) to prioritise or whatever but the upshot is that you end up with a score on each dimension and then i guess there is some arbitrary threshold for when a score on a dimension is 'clinically significant'. if you are very very very lucky you might score clinically significant on about 9 dimensions as i was which greatly thrilled my psychologist because she figured she had about one or two years worth of work to do! (joke kinda semi sorta).

i'm skeptical about tests as you can see... if you or your therapist like to worry about all these little boxes that you might potentially fit when looking at you squinting then i guess it is an interesting exercise, however. almost like... reading hororscopes or runestones IMHO...