The Myers-Briggs test should only be taken once without the subject of the test fully aware of the the system. Otherwise you get a lot of false numbers.
People often read the types, fixate on the one they relate to, or aspire to be like, and answer the questions that obviously fill the criteria.
Online, everybody is an INTJ, because INTJ is fucking cool. (Especially among freedom lovers and geeks.) Compound this with the fact that "real" INTJ's are stat whores of the worst sort, and your demographics get messed up P.D.Q.
Here's a fun example:
Curiosity, cleverness, skill, communication; making connections with surroundings, trying to "figure things out"; the first display of intelligence by embodied spirit. Talkative , communicative, sociable; loves to interact with others ; unemotional, impersonal, ruled by "rationality"; requires great mental stimulation, curious to a fault; the Devil's Advocate.
ENTJ right? Wrong.
That's the description of "Gemini" the Zodiac sign.
Tests like this are effected not only by the simple answers to questions, but by how the person taking the test wishes to be perceived.
For example:
IRL, Myers-Briggs says John Shaw is an INTJ. John shaw likes the idea of INTJ and that's why the result was INTJ. The fact of the matter is, if you know me for more than five minutes, you will know that the most difficult thing about being near me is that fact that I NEVER FUCKING SHUT UP. This is not the behavior of an INTJ.
The reality is, is that John Shaw is a big ole' loudmouth ENTJ. The test sez otherwise because I'd like to be the introspective, deep thinker, when in reality my mind works more like a carpet bombing than Ninjutsu.
I take some solace in the fact that I'm still pretty smart, if not introverted.
This is also an important factor.
http://en.wikipedia.org/wiki/Forer_effect