Replying to this statement, I would like to give some quotations from The Discipling Dilemma, chapter 2:
The MBTI was administered to 304 members of churches of Christ that are not a part of the discipling movement. There were 150 females and 154 males in this sample. They were given the same past, present, and future instructions as those used in the study of the Boston Church of Christ. Not a single one of these individuals changed on all four of the MBTI scales or even on three of them. Three people changed on two of the scales and 33 changed on one of the scales. All 36 who showed any change at all in MBTI scores had very low preference scores on the scales involved in the changing scores. This level of change is about what one would expect under these conditions from random test error. The MBTI, after all, is not a perfect indicator. In this comparative study, however, there was no observable pattern in the few changes that took place. Those who changed from Extravert to Introvert, Sensor to Intuitor Thinker to Feeler, or Judger to Perceiver were balanced by others changing in the opposite direction. The overall distribution did not change.
The people who have changes of scores on MBTI scales are those who had very low preference scores on the scales involved in the changing scores. In addition, these changes do not indicate that their personality types were changed. These changes are caused by random test error. Another important point is that there was no pattern in these changes.
However, the changes of members of ICC and some non-Christian cults were very different.
The first result of this study to be discussed is the observation that a great majority of the members of the Boston Church of Christ changed psychological type scores in the past, present, and future versions of the MBTI. Among the 835 individuals who took all three forms of the MBTI, less than five percent showed no change at all and less than seven percent had the same past and future type. Among the rest, a comparison of past and future types showed that almost 20 percent changed on one MBTI scale, 35 percent changed on two, over 26 percent changed on three, and over 12 percent changed on all four scales, thus experiencing a total reversal of type. The mean number of scale changes was 2.18 among the 835 members of the Boston Church of Christ who took all three forms of the MBTI. The present distribution was significantly different from the past distribution. The difference between past and future type distributions was highly significant.
The first result is that most members of ICC experienced changes of psychological type scores while only few members of Churches of Christ had some changes of scores.
A second result of this study that must be noticed is that the observed changes in psychological type scores were not random since there was a clear convergence in a single type.
There was a clear pattern of changing from introversion to extraversion, from intuition to sensing, from thinking to feeling, and from perceiving to judging.
Those who were the least likely to change were those who already were ESFJs. They averaged only 0.32 changes on the four MBTI scales. Those who were the most likely to change were those who started as the opposite type, INTP. They averaged 3.55 changes on the four scales. There was a strong positive correlation between the number of differences between a type and the ESFJ model, on the one hand, and the mean number of changes on the four MBTI scales on the other hand. The more a person differed from the ESFJ model, the more likely that person was to change on more of the MBTI scales.
There was a clear pattern of changes of personality types in ICC while there was no pattern of changes in Churches of Christ.
So, the changes of personality type scores outside of cults are very low. They are caused by random test error and not by actual changing of personality types. These changes do not have any pattern.
Flavil Yeakly wrote that the true type is inborn and does not change. What may change is the result of MBTI testing.
I used MBTI and some other tests of psychological types for the time before I joined the cult, for the time in the cult, and for the present time. I had the same results each time.
Before the cult I was INTJ. In the cult, I was ESFJ. Now, I am INTJ. As I have mentioned, ESFJ was the personality type of the cult leader. I had almost the same scores before the cult and for the present time. In both cases, I got very expressive preferences for introversion, intuition, and thinking. However, I had changes in all these scales to extroversion, sensing, and feeling. These changes are impossible outside of cults. In addition, after the cult, I returned to the same type and almost to the same scores as before the cult.