There are still some things I want to make clear regarding personality types and personality tests like MBTI, Keirsey, and other. Discussing these tests and personality types with other people, I noticed that some people do not really understand what these tests measure.
1. All the personality tests have instruction to answer the questions as you USUALLY act or think, not as you WOULD LIKE to do.
2. These tests measure PREFERENCES, not the functions or abilities. This means that, for example, if a person is scored as an introvert, he or she still may act as an extravert in some situations, but he or she usually PREFERS to act as an introvert. This person may or may not have an ability of extraversion. However, his/her preference is to act as an introvert. His/her ability for extraversion is less developed than his/her ability for introversion. However, this does not necessary mean that he or she does not have any ability for extraversion. So, it is the preference for one or the other function that makes the dichotomy, not the functions themselves. Many people can use both functions in the pair, however, they still prefer to use one of them.
Some people do have low scores on some scales. There may be two reasons for that mentioned by Yeakley:
1. Some people who have low scores are not sure who they are. Their preferences are just very undeveloped.
2. Some people who have low scores have made efforts to develop their less developed functions to the extent that both functions in the same pair became almost equally developed. Then, these people may have some difficulty with preferring one function from the pair.
I think there may be one more reason - some people try to answer how they would like to act and think, not how they usually act and think.
Actually, I do not think that MBTI, Keirsey, and similar tests are perfect. There is one thing that puzzles me with Keirsey. If a person has equal scores for E/I, he/she is scored as I; if he/she has equal scores for S/N, then, he/she is scored as N; the same is with T/F and J/P. Each pair has even number of questions, so it is possible to has equal scores for each alternative. To me, it would be logically to have odd number of questions for each pair. Then, the scores would never be equal. Probably, MBTI and other tests have the same problem.
MBTI and probably Keirsey do not have the normal distribution. Actually, this is quite good. Many psychological tests, for example, IQ tests and EPI have normal distribution. IQ tests have the mean equaling 100 and 3 sigma equaling 40. This means that the average IQ is 100 and 99.7 percent people have IQ between 60 and 140. Most people have IQ around 100 and less people have IQ significantly different from 100. EPI is a personality test, and it has the normal distribution for both scales.
If MBTI and Keirsey had the normal distribution, it would mean that most people have very low scores, close to zero. Then, most people would not be able to find out their personality type from these tests. Fortunately, there are not so many people who have this problem.