As the degree to which a test measures what it is supposed to measure, validity is a difficult property to evaluate in a test. Consider tests of intelligence. Many people are skeptical of the results of these tests. Some people are concerned that the tests measure only "book learning" and do not test "common sense." Other people feel that
intelligence tests have cultural, racial, and gender biases. Therefore, to conclude that a test is a valid measure of intelligence, it must be shown that the test measures intelligence independent of the testee's education, culture, race, and sex.
There are many ways to evaluate the validity of the MBTI test. I will examine two important pieces of evidence. First, we can determine if the four dimensions described in the MBTI theory really exist. This is accomplished by using a statistical procedure known as "factor analysis." Secondly, we can determine whether knowing a person’s
MBTI type really allows us to predict how that person will perform under different circumstances. The importance of this question of validity is obvious. It must be shown that there is a consistent and meaningful relation between
MBTI results and success in career placement.
Factor Analysis. The factor analysis is a type of statistic procedure that consists of making an analysis of the correlations among the questions in the test. If the MBTI theory is correct, three results should come from the factor analysis. First, the results should show that there are four clusters, or factors, of questions. Each of the questions within a factor will be highly correlated with the other questions in the factor. Moreover, the questions within the factor should be related to the MBTI dimension that is measured. For example, a question like "I like to be the life
of a party" should be in the factor related to extroversion-introversion.
Secondly, we would expect each factor to be independent of the other factors, inasmuch as the MBTI theory states that each of the four preference dimensions stands alone. That is, questions within one factor should not correlate with questions in the other factors. If two factors are correlated, it means they are probably measuring the same thing.
Finally, we would expect that the factors would account for most of the differences among individuals. Here is an example that will illustrate this point. A test consisting of many unrelated questions would produce no consistent pattern in the differences among the people tested, and we would say that there is a large amount of measurement error. If, however, the questions are highly related, there should be consistent patterns that can be accounted for by the test, and the measurement error would be relatively small.
Research on the factor analysis of the MBTI has not produced convincing results. In one study, based on the results of l,29l college aged students, six different factors were found.10 In addition, the study authors found a high level of measurement error. Specifically, 83 percent of the differences among the students could not be accounted for by the MBTI. The results led the authors to the conclude that the factors found in the statistical analysis were inconsistent with the MBTI theory. In other studies, researchers found that the JP and the SN scales are correlated with one another.
In sum, the statistical analysis of the test does not support the theory used to describe the MBTI. Relation Between MBTI Type and Occupation. Many people have examined the relation between type and occupation by examining the proportions of type within each profession. For example, one might observe that many
elementary teachers are ESTJs and conclude that ESTJs prefer to be elementary school teachers or to work in a related occupation. Although it sounds appealing, such a conclusion runs into many fundamental problems. First, we need to examine the normative data to judge the relation between type and profession. For example, the
proportion of ESTJs in the teaching profession is the same as the proportion of ESTJs in the general population, or 12 percent. This similarity suggest that there is nothing special about the type of person who becomes an elementary school teacher.
Another problem stems from jobs that are dominated by men or women. Nursing is a good example. If we compare the distribution of type for nurses against managers, there appears to be a different pattern of type. We could conclude that certain types are more likely to enter nursing while other types are more likely to become managers.
There is, however, an alternative interpretation. Nursing has been and remains a profession dominated by women. There is a high correlation (r = .91) be tween the percentages of types for all women and people in nursing. The correlation between all men and people in nursing is, by contrast, small (r= .21). In a male dominated profession such as management, there is a high correlation between types in management positions and men in general (r=.92), but a smaller correlation for women (r = 60).12 If it is true that certain types are attracted to certain professions, then
these correlations should be much smaller. Instead, these data suggest that the proportion of MBTI types within each occupation is equivalent to that within a random sample of the population.
Finally, there is no evidence to show a positive relation between MBTI type and success within an occupation. That is, there is nothing to show that ESFPs are better or worse salespeople than INTJs are. Nor is there any data to suggest that specific types are more satisfied within specific occupations than are other types, or that they stay longer in one occupation than do others.
In summary, it appears that the MBTI does not conform to many of the basic standards expected of psychological tests. Many very specific predictions about the MBTI have not been confirmed or have been proved wrong. There is no obvious evidence that there are 16 unique categories in which all people can be placed. There is no evidence that scores generated by the MBTI reflect the stable and unchanging personality traits that are claimed to be measured. Finally, there is no evidence that the MBTI measures anything of value.
