I don't know who the heck "Jimmy" is in this link, but he calculates percentages of the population based on MBTI. He says he uses Kiersey as a reference. If this is correct then for every one INxx there should be on average six ISxx.
INTP, INTJ, INFP, INFJ = 1% each
ENTP, ENTJ, ENFP, ENFJ - 5% each
ISTP, ISTJ, ISFP, ISFJ = 7%, 6%, 5%, 6%
ESTP, ESTJ, ESFP, ESFJ = 13% each
If anyone has any other data or links concerning population percentages and MBTI, post them here. Also, if there is evidence to refute any of the info, be sure to include that as well.
MBTI Population Percentage Thing