The 1991 scientific view of the MBTI.
In 1991 the National Academy of Sciences review committee concluded at the time there was "not sufficient, well-designed research to justify the use of the MBTI in career counseling programs". However, this study also based its measurement of validity on "criterion-related validity (i.e., does the MBTI predict specific outcomes related to interpersonal relations or career success/job performance?)." The ethical guidelines of the MBTI assessment stress that the MBTI type "does not imply excellence, competence, or natural ability, only what is preferred."
My observations is that is a close correlation between types and happiness (or otherwise) in careers.
My circumstantial observations would also equate F & T with IQ tests ability. Under 100 and you are F.