I have come across a number of Personality theories. There are even disciplines of personality theories, dividing these theories according to the assumptions they are based upon. The most accepted/used theories seem to be Big 5 and Myers Briggs Type Indicator (MBTI). However, these theories too use traits to determine types among people.
For example, the five traits Big 5 uses to distinguish seem to be of very limited scope. Also, measuring between traits like Introversion and Extroversion, using some random questions which have polar opposite choices seems to be fitting into a box sort of thing. There seems to be no scientific method while testing to determine whether people fall into one region or other - for all the defined traits.
By scientific determination, I mean one could use methods like the one laid out in Cerebral Blood Flow and Personality: A Positron Emission Tomography Study to determine between, say, Introversion and Extroversion traits. I am not sure whether the other traits have such methods researched enough to distinguish between them.
Is there any Personality theory that is purely based on scientific grounds?
Is there any existing personality theory (that is being researched), that could one day be backed up by scientific research? I think Big 5 might come under this category. But any evidence to the above regarding any theory will be appreciated. Thanks!