I just read about this in THIS BOOK based on the five-factor model of personality.
Anyway, it presents with a wonderful graph involving what looks like an upside-down bell curve. The Y-axis is degree of consistency on a trait and the X-axis is level of the trait (low to high).
So what does this mean? Using extroversion as an example, if someone scores very low or high on this, it's pretty much definite that they consistently like extroverted or introverted stuff. However, if someone scores as a perfect ambivert (50 out of 100), this could come from two extreme results and anything inbetween. One extreme would be nothing but middle answers on all questions having to do with this trait. The other extreme would be the result of 50% lowest answers and 50% highest answers.
With the MBTI, people are often undecided about a trait, and now I see that this could very possibly be the result of being moderate with a trait, or it could be the result of bouncing between both pretty regularly.
With extroversion you would have either someone who likes to switch between larger social gatherings and solitude, or someone who doesn't like too much of either one and prefers having a one to four friends and family members around most of the time.