Predictive Index® Technical Overview
If you have ever heard of the phrase “the people make the place”, then you’ll understand why the use of personality assessments in business and industry continues to grow rapidly. Since approximately the late 1980’s, the academic study of personality and the application of personality theory toward the solution of key organizational challenges has undergone a marked renaissance. Interest in personality has also expanded past traditional domains such as personnel selection and hiring (Roberts & Hogan, 2001) to touch upon diverse areas such as the influence of personality on team performance, leadership, organizational culture and climate, entrepreneurship and innovation, stress and well-being, work motivation, job satisfaction, and a host of others. Personality assessments tap into each employee’s unique “behavioral DNA,” yielding key insights into people’s individual drives, temperaments and motivations (e.g. why I might prefer analyzing financial statements for hours on end, while you’d prefer to be out of the office developing personal relationships with customers.) Hundreds of empirical research studies, conducted in a wide variety of settings, have conclusively demonstrated the quantitative connection between personality and job performance (Barrick & Mount, 1991; Barrick, Mount & Judge, 2001). Quite simply, scores on well-developed personality measures are stable across time and situations, and are useful predictors of behavior and job performance.
Personality has been defined in many different ways by a variety of theorists.
Harvard’s Gordon W. Allport, in his seminal textbook on the field (Allport, 1937), defined personality as:
“Personality is the dynamic organization within the individual of those psychophysical systems that determine his unique adjustment to his environment.”
Another pioneer in the field of personality, Raymond B. Cattell of the University of Illinois viewed personality as (Cattell, 1945):
“That which permits a prediction of what a person will do in a given situation. The goal of psychological research is to establish laws about what different people will do in all kinds of social and general environmental situations.”
MacKinnon (1944) suggested that personality has two conceptually distinct definitions. Used one way, personality refers to the distinctive and unique impression that one makes on others. This perspective refers to personality from the viewpoint of the observer, and is functionally equivalent to a person’s reputation. Used in a second way, personality refers to the structures inside of a person that are useful in explaining why a person creates a particular impression on others.
This is personality from the perspective of the actor, concerned with how a person perceives him or herself, and is functionally equivalent to a person’s identity. This “dual definition” of personality is also espoused by more contemporary personality researchers and theorists (e.g. Hogan, 2004). The Five-Factor Model (FFM) of personality normally attributed to Tupes and Christal (1961) suggests that many existing personality constructs can be organized in terms of five broad traits: (1) Extroversion, (2) Agreeableness, (3) Conscientiousness, (4) Emotional Stability, and (5) Openness.
The Predictive Index® (PI®) is a theory-based, self-report measurement of normal, adult, work-related personality, and has been developed and validated exclusively for use within occupational and organizational populations. The PI® employs a free-choice (as opposed to forced-choice) response format, in which individuals are presented with two lists of descriptive adjectives, both containing 86 items, and are asked to endorse those which they feel describe them (the “SELF” domain), and then those which they feel coincide with how they feel others expect them to behave (the “SELF-CONCEPT” domain). Summing across these two domains yields a third implied domain (the “SYNTHESIS”), which can be interpreted as reflecting an employee’s observable behavior in the workplace. The assessment is un-timed, generally takes approximately five to ten minutes to complete, and is available in paper-and-pencil, desktop and internet formats. The PI® has been in wide-spread commercial use since 1955, with minor revisions to the assessment occurring in 1958, 1963, 1988 and 1992. These minor revisions were undertaken to both improve the psychometric properties of the PI® and to insure that each of the individual items on the assessment conformed to appropriate and contemporary language norms.
The scoring of the Predictive Index® checklist produces a behavioral pattern with three elements, known as the Self, the Self-Concept and the Synthesis. The Self measures a person’s natural, basic and enduring personality. The Self Concept measures the ways in which a person is trying to modify his or her behavior to satisfy perceived environmental demands. Lastly, the Synthesis, which is a combination of the Self and Self-Concept, measures the ways in which a person typically behaves in his or her current environment.
The Reliability of PI® Reliability refers to the consistency or stability of a measure (Nunnally & Bernstein, 1994). If the concept being measured is assumed to be consistent, such as a personality trait, then the measure should yield similar results if the same person responds to it a number of times. If the concept being measured is assumed to be inconsistent, such as mood, then the measure should yield dissimilar results if the same person responds to it a number of times.
One way to estimate reliability is by computing the measure’s “test-retest reliability”. Test-retest reliability is perhaps the easiest assessment of a measuring device’s reliability to conceptualize and understand. Using the same group of people, a construct is measured at two separate points in time and then the two sets of scores are compared. This technique yields a correlation often known as the coefficient of stability, because it reflects the stability of test scores over time. If the measure under study is reliable, people will have scores that are similar across trials. Note that the shorter the time interval between administrations of the test (e.g. two weeks versus three months), the higher will be the test-retest coefficient.
PI® Measurement and Scaling Structure The PI® assumes that a single personality dimension is being tapped by each PI® factor scale. For example, Factor A is expected to assess the broad personality trait of dominance. Nuances of this trait are captured in the individual adjectives, and are summed to broadly define Dominance. This assumption of unidimensionality within each factor is examined empirically in this evaluation. According to classical test theory, the variability in an item set can be separated into shared, or “true score” variance and unique, or “measurement error” variance (see Allen & Yen, 2002). In other words, differences between individuals’ responses to an adjective can be attributed to actual differences in the personality dimension it is designed to measure (“true score”) and to unrelated influences (“measurement error”). For instance, the word "popular" can evoke images of specific attributes of an individual's past schoolmates in addition to more abstract notions of popularity associated with extroversion. The degree to which an item is influenced by factors other than that intended is referred to as measurement error. All psychological assessment instruments contain some proportion of measurement error.
In the classical test theory conceptualization, individual items are evaluated in an effort to discover the extent to which they contribute true score variance to the factor score estimates. Note that the adjectives reflecting each PI® factor are words of degree - not true opposites. For example, a peaceful person can be somewhat belligerent. Item Response Theory (IRT), scaling and other measurement models assume that items are ordered according to their ability to detect differences in degree at different points along the underlying personality continuum. In other words, one item may be endorsed at very low levels of a personality dimension and, as the degree of the dimension increases, another item may also be endorsed. Because psychological dimensions cannot be directly observed but must be inferred from measurement characteristics of the items in the assessment instrument, changes in the measurement model (item changes, shifts in the proportion of measurement error, etc.) imply changes in the interpretation of the factor. Meaningful comparison of factors requires the assumption that factor scores have the same meaning in both the Self Concept and Self domains. In other words, scaling must be identical across domains if one is to say, for instance, that an individual perceives himself to be less formal than he feels others expect him to be. Since factor scores are composites of item sets, this assumption implies that each item reflects a personality dimension in the same way in the two domains and has a similar proportion of measurement error. The measurement properties of the items underlying the construction of factor scores allow us to explicitly test the assumption of equivalence of scale across domains.
A key feature of the PI® is that factor scores can be used to construct an individual’s personality profile, or factor pattern. Because the relative intensity levels of the four personality dimensions measured by Factors A through D are essential to the interpretation of personality profiles, there is an implied assumption of comparability of the metric of factor scores. Said differently, personality tendencies representing a similar degree of intensity should be plotted at similar points on the PI® factor plotting template. Only by making this assumption regarding the scaling of the factors can one say, for example, that an individual has a higher tendency toward dominance than extroversion (High A/Low B). Principal component analysis, a special form of exploratory factor analysis, can be used to evaluate the assumption of unidimensionality in the sets of items comprising each PI® Factor. Utilizing the same sample of 3,991 applicants and job incumbents referenced above, eigenvalue decomposition was used to create a scree plot for each item set, which shed light on the optimal number of components (factors) that can be extracted. Scree plots obtained from models for each PI® factor showed evidence of unidimensionality. As can be seen in the Appendix of this document, Figures 1 (Self-Concept) and 2 (Self), there is a decidedly sharp drop-off after the first eigenvalue for each of the Factors A through D, followed by a relatively flat slope.
Sample descriptors - here are two of the seven PI profile types converted directly to job post verbiage.
1) Is your favorite day on the job when you get to work with other people in a group? Do you find it exciting to meet new people? You are a well-liked and enthusiastic contributor to your team. Even in difficult situations, you have great tact and charm.
2) Do you like to face challenges and make decisions on your own? When you identify a goal is your first instinct to start NOW? You like it best when you can focus on results, challenge the status quo and control resources to make things happen. You’re a decisive self-starter with the competitive drive to win.