The following analysis is based on a review of the MBTI website as well as several scientific articles.
Overview
As a test of personality, the MBTI is not comprehensive, produces scores inconsistent with its theory of distinct personality types, and lacks both reliability and validity. In contrast, the RMP was developed scientifically, has been validated by independent researchers, and has passed stringent peer review for publication in scientific journals. Numerous studies have provided evidence for the reliability and validity of each of the 16 RMP scales.
What does each test purport to measure?
The MBTI was designed as a measure of personality type. Based on a theory by Swiss psychiatrist Carl Jung that personality types are formed by innate preferences for extraversion versus introversion, thinking versus feeling, sensing versus intuition, and judging versus perceiving, the test assesses which of 16 personality types best applies to an individual.
The RMP was designed to measure motivation – specifically, how an individual prioritizes each of 16 basic desires. According to the theory of motivation proposed by Professor Steven Reiss, our basic desires determine our values, influence the development of our personality traits, and predict our behavior.
Comprehensiveness
An analysis of the 93 items on the MBTI suggests that the test measures a narrow range of personality traits: Nineteen items assess orderliness, 17 items assess friendliness, and 13 items assess curiosity. Thus, more than half of the test questions measure only three traits. Few or no items pertain to the assessment of other important personality traits such as self-confidence, loyalty, honesty, kindness, materialism, frugality, attention seeking, and risk-taking. Independence, achievement, and aggression, for example, are assessed by only one, one, and three items, respectively – not nearly enough to be valid. In short, the MBTI does not provide a comprehensive assessment of personality.
The RMP has 128 items which measure 16 basic desires. The initial draft of the questionnaire included more than 500 items reflecting every imaginable goal that might motivate someone. After paring this list to 328 items by eliminating redundancies, Professor Reiss conducted a series of studies with four separate samples of subjects in which he used a statistical technique called factor analysis to interpret the data. The end result was 16 scales, each comprised of eight items. Thus, the RMP is a comprehensive measure in that the scales are based on a statistical analysis of how thousands of people responded to hundreds of items about what motivates them.
Statistical Structure
A test taker’s score on the MBTI is based on his preference for each of four dimensions. For example, people are classified as either extroverts (E) or introverts (I). If this classification system were valid, we would expect that scores on the MBTI would produce two different curves – one curve representing all of the extroverts, and the other curve representing all of the introverts – with little or no overlap between the two. In other words, we would expect a bimodal distribution of scores rather than a normal distribution of scores. In fact, scores on the MBTI are not distributed bimodally. Most people score somewhere between the two extremes, thus suggesting that the score of a test taker classified as an E may be quite similar to that of a test taker classified as an I.
The RMP measures personality traits along a continuum, the method preferred by researchers. For each of the 16 scales, most test takers’ scores are clustered around the mean, with fewer and fewer scores found the farther one moves away from the mean. Thus, RMP scores are distributed normally, which is consistent with observations of real-life behavior. Consider, for example, the Social Contact scale. Most people – those with an average desire for Social Contact – show a mix of traits characteristic of extroverts and introverts; at times they are friendly and outgoing, while at other times they are private and serious. A few people – those with a strong desire for Social Contact – are almost always friendly and outgoing as they seek to maximize their opportunities for peer companionship. Similarly, a few people – those with a weak desire for Social Contact – are almost always private and serious as they seek to avoid most opportunities to interact with peers. Unlike the MBTI, scores on the RMP are consistent with its underlying theory that personality traits are distributed normally.
Reliability
Reliability refers to the degree to which a test produces stable and consistent results. Two common ways to assess the reliability of a test are test-retest and internal consistency. Test-retest reliability measures the consistency of results when the same test is repeated on the same sample of subjects at different points in time. Internal consistency refers to the degree to which each item on a scale measures the same construct.
Several studies have shown that between 39% and 76% of respondents are classified into a different MBTI type after a test-retest interval of only five weeks, thus calling into serious question the reliability of the assessment.
Studies assessing the internal consistency of each scale on the RMP revealed results that range from acceptable to excellent. Further, the test-retest reliability for each of the RMP scales after a four-week interval was found to be acceptable to good. These results provide solid evidence for the reliability of the RMP. Unlike the MBTI, respondents’ RMP results are likely to remain stable and consistent over time.
Validity
Validity is the degree to which a test measures what it was designed to measure. Concurrent validity and criterion validity are two common methods used to assess the validity of a test. Concurrent validity refers to the degree to which a test’s scales are positively correlated to similar scales on other assessments. Criterion validity refers to the extent to which a measure is related to an outcome.
Studies of the concurrent validity of the MBTI have found that only the I-E scale is highly correlated with other scales that measure the same concept. Further, researchers have failed to obtain evidence that MBTI personality types are associated with success in an occupation, satisfaction with a career choice, or longevity in a position, findings that cast serious doubt on the test’s criterion validity.
Evidence for the concurrent and criterion validity of the RMP has been reported for each of the 16 scales. The Honor scale, for example, was demonstrated to have concurrent validity because it was found to be positively correlated with similar scales on the Big Five and the Purpose in Life. Further, the Honor scale was demonstrated to have criterion validity in that military officers and religious people scored above average for this basic desire for upright character. For each of the 16 scales on the RMP, data from at least three studies provided confirmation of the test’s validity. For some scales (Curiosity, Honor, Idealism, Power, Status, Tranquility, Vengeance), the evidence for validation was based on studies ranging from five to 11 in number.
Sources of Evidence
It is important to consider the source of the evidence when evaluating the scientific merits of a test. The studies that produced data critical of the MBTI were conducted by independent researchers and organizations such as the Educational Testing Service, the National Academy of Sciences, and the United States Army Research Institute. Most of the research supporting the MBTI has been generated by the Centre for Applications of Psychological Type, an organization run by the Myers-Briggs Foundation, and the studies then were published in the Centre’s own journal, thereby raising questions of bias and conflict of interest.
Professor Reiss’s studies on the RMP passed stringent peer review by other researchers in order to be published in scientific journals unrelated to IDS Publishing Corporation. Moreover, the RMP has been validated by independent researchers such as Professor Thomas Mengel of the University of New Brunswick and Professor Kenneth R. Olson of Fort Hays University.
Test Developers
Katherine Briggs became interested in the field of personality after observing marked differences between the personality of her future son-in-law and that of other family members. She then proceeded to develop a theory of personality types based on her reading of biographical novels. After graduating from Swarthmore College, Isabel Briggs Myers joined her mother in her quest to develop a measure for matching women to jobs in which they would be “most comfortable and effective.” Neither Briggs nor Myers had any formal training in psychology, test construction, or statistical methods.
Professor Steven Reiss’s interest in studying motivation was stimulated by a life-threatening diagnosis. Realizing that the field of motivation suffered from the lack of a scientific measure, he developed the RMP for the purpose of advancing knowledge about human nature. Professor Reiss graduated from Dartmouth College, completed a fellowship at Harvard University, and earned a doctoral degree in psychology from Yale University. Prior to developing the RMP, he created two other widely used assessments: the Anxiety Sensitivity Index and the Reiss Screen for Maladaptive Behavior.
Conclusion
Historically, the MBTI represented a significant departure from prevailing psychodynamic theory in which personality was assessed through the lens of psychological disorder. Briggs and Myers deserve credit for introducing the viewpoint that differences in personality are the result of normal variations, and their work should be recognized for the role it played in making the study of the normal personality an important topic. Nevertheless, the overwhelming majority of independent researchers who have studied the MBTI have concluded it lacks utility. In contrast, the RMP’s strong scientific underpinnings allow for a reliable and valid assessment of an individual's values, personality traits, and behavior - in short, for understanding why people do what they do.