Mark Majors, Ph.D. — Author of the Majors Personality Type Inventory™
Dr Mark S. Majors is a counseling psychologist with extensive psychometric credentials. He is the author and developer of the Majors PTI™, Majors OEM™ and Majors PT-Elements™) and principal developer of the Interstrength® X-Styles Assessment. He provided the data analysis on the 1994 Strong Interest Inventory and the MBTI® Form M and Form Q, developed the IRT scoring for the MBTI® Form Q, and co-authored the MBTI® Form Q Manual. In addition to the test development, Mark trains pastoral counsellors with an emphasis on the use of personality assessment for conflict resolution through the acceptance of differences and personal growth. He has developed and presents leadership training seminars that train leaders to serve others by using personality and individual differences to facilitate optimum performance. He has provided 19 years of successful individual and couples/marital counselling and coaching using personality differences and has authored numerous books, manuals and articles on personality differences and biblical psychology. He received his Bachelor of Science and Master of Science degrees in psychology from Iowa State University and his PhD in counselling psychology from the University of Nebraska–Lincoln.
The validity of any instrument is the evidence that it measures the constructs that it is purported to measure.
The MajorsPTI was developed by selecting items, which demonstrated that they were consistent with the known personality type of knowledgeable individuals (criterion based validity).
In other words, each item had to establish its own validity to be included on the psychological type dimension that it was intended to be on. A second form of validity is construct validity. This method tests the structure of the items and scales to prove that the measurement model that they represent is valid.
Best-fit is not an illusion! The only way to prove that a measure of psychological type is accurately measuring psychological type is with people who know their type. The key point is that the individuals involved in this form of research must know their type. This is a process that involves time and education. People need to have experiences where they test their own personal type hypothesis against the reality of their lives.
To apply the best-fit method of establishing validity to the MajorsPTI a sample of 203 individuals was collected from midwestern, southwestern and southeastern cities. For the data to have been accepted for use in the best-fit study for the MajorsPTI each person had to report their best- fit type. Further, these participants had to present information on how they had come to know their type, and how long they had been studying type. Most or 74% (type aware) had been through some formal training or workshop that had introduced them into the thinking and conceptualization that is psychological type. The other 26% (type naïve) were individuals who had experienced type in a feedback session followed by months of experience and personal investigation, or where personally known by the MajorsPTI test development team who helped them to establish their best-fit type. Each participant had to report their confidence that they knew their type across each of the four scales (1 no confidence to 10 complete confidence). Table 6 presents the best-fit data for the MajorsPTI.
All of the disagreements between MajorsPTI results and Best-fit type were found to occur on one scale at a time (there were no occurrences of two type letters being different for an individual). All of the disagreements occurred when the continuous scores were less than 5 indicating slight clarity of preference. This occurred in both type naïve and type aware individuals.
In 2009 another best-fit sample (N = 204) was collected in the publisher data from professional user administrations. In this sample the professional had to confirm the type that the individual client identified as their best-fit after feedback and consultation. The accuracy rate was 92.5% for all four letters of the type code. No individuals were mistyped on more than one dichotomy and the errors were distributed across all four of the dichotomy scales. There are no other measures of Jungian type that approach this level of accuracy. These results indicate that the MajorsPTI is very accurate in assessing psychological type.
Another method of assessing the validity of an instrument is known as construct validity. This form of validity is assessed by using factor analysis to confirm the existence of the constructed scales or factors. The items from the MajorsPTI using the balanced by type and sex sample (N = 230) were subjected to a principal axis factor analysis using a Promax rotation. All of the items were allowed to freely load on 4 factors. In the factor analysis, the hypothesized model of the four scales and the items that formed them are expected to emerge. This matching of the relationships found between the variables to the scales establishes the validity of the underlying constructs. Simply put, it tests whether the items on the four scales really confirm the four-scale model that is intended.
Results of the factor analysis indicate that the MajorsPTI four scales are confirmed in the data. All of the items loaded strongly on their intended scales. The range of factor loadings was .57 to .84 for E/I, .43 to .81 for S/N, .51 to .75 for T/F and .365 to .83 for J/P. Cross loading (an item loading strongly on two or more factors) occurred in two J/P items that also loaded on S/N.
Another indicator that a measure has been properly constructed is an evaluation of the relationship between the scales. The scales of measures of psychological type are to be independent, or the scales are measuring different constructs. The results of Pearson product moment correlation analysis across the four MajorsPTI scales are presented in Table 7. The data indicates that the S/N and J/P scales correlate r = .32. While this correlation is the highest one occurring between any of MajorsPTI scales, it does not however, represent more than a very weak relationship.
Results of validity analysis indicate that the MajorsPTI measures accurately the four psychological type constructs that it was developed to measure. The results of best-fit analysis are of particular importance due to its clear indication that the results of the MajorsPTI instrument are consistent with the reality of the individual. Given the reported reliability and validity in this chapter, the MajorsPTI stands as an excellent measure of personality type.