Actually, most scales of introversion and extroversion (some people spell it extraversion) are quite poorly validated, and that especially goes for the Myers-Briggs questionnaires.

http://skepdic.com/myersb.html

http://www.indiana.edu/~jobtalk/HRMWebsite/hrm/articles/deve...

I accept the idea that some people on particular occasions enjoy the company of other people more than others, but it's considerably less clear that this is even a stable trait, rather than a state, on the individual level, and many of the inferences drawn from classifying a person as "introverted" or "extroverted" are highly debatable.