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Thomas PPA is a forced choice ipsative instrument used as a means to describe an individual in a self referential way and may provide information of importance and value to employers making personnel decisions.

The Theory behind Thomas PPA

Personal Profile Analysis (PPA) has its original impetus from the writings of Marston (1928, 1931) [1] who postulated a theory of human behaviour as a function of two bipolar dimensions, one external and the other internal.

These two dimensions provided a matrix from which the individual’s typical pattern of interaction could be described through four characteristics: Dominance, Inducement, Submission and Compliance (DISC). Marston’s theory assumed that most people are capable of showing all four of these patterns at different times. However, individuals develop, through learning and reinforcement, a style of life which places particular emphasis on certain aspects of behaviour and less on others. Further research by others in the 1950s confirmed this proposal that behaviour can be measured along the two axis/four dimensions as suggested by Marston. [2]

Applying DISC in the workplace

In the late 1950s and early 1960s, Dr. Thomas Hendrickson of TM Hendrickson and Associates, developed Marston’s insights further to produce the Thomas Personal Profile Analysis for the work place.[3] PPA has since gone through rigorous tests to determine its consistency and validity. Studies done in the UK have compared PPA with 16PF and OPQ assessments and found that the four Dominance, Influence, Steadiness and Compliance domains are clearly recognisable when defined by the factor names of other inventories [4]

The PPA is a forced choice IPSATIVE instrument. This means it describes the individual in a self referential way and is regarded as providing information of importance and value to employers making personnel decisions. The Thomas PPA attempts to determine whether individuals see themselves as characteristically seeking out and/or reacting to work place situations that they perceive as supportive or challenging and to reveal if the response pattern is active or passive.

Thomas PPA is a self administered forced choice adjective checklist consisting of 24 tetrads of descriptive words from each of which applicants are asked to select which they believe describes them most and which least. The words chosen in Hendrickson’s first experiments were based on Marston’s definitive work.[5] As far as possible the words selected corresponded to Marston’s model.

Original Construction Methodology

The first empirical trials were conducted by Hendrickson on a small group of 115 people (67 males / 48 females) in 1958.[6]

Frequency distributions of responses were recorded and words were re-combined in tetrads such that each tetrad contained a word relating to each dimension. Moreover, attempts were made to combine words of relatively equal response strength in order to reduce the effects of social desirability in response patterns. High response words were grouped together with other high response words, low response words with other low response words. 76 of the original 96 words were absorbed in this manner and five extra tetrads were constructed to bring the total once more to twenty four. Of the words retained 39% are the same as in Marston’s original model.

Test, Revise, Retest

The revised PPA form was administered to a larger and more representative sample group of 500 (388 male/112 female).

A random sample of 100 was drawn from this group to determine inter-correlation among the four factors. The results indicated that the Personal Profile Analysis had a satisfactory internal consistency when assessed in this way.

To eliminate non discriminating items from the scoring key, an item analysis was initiated. A random sample of 185 (130 male/55 female) was drawn from a population of 1200. The internal consistency was confirmed and the scoring key adjusted. At this stage, the Marston dimension of SUBMISSION was changed to STEADINESS and the Marston dimension of INDUCEMENT changed to INFLUENCE.

A random sample of 100 (75 male/25 female) was selected to test the new scoring key and the results correlated against the original trials. To assess the reliability of PPA, test/retest trials were conducted on a sample of 72 (47 male/25 female) with the new scoring keys.[7]

Validity and Consistency

It is generally accepted that efficacy of tests, including behavioural and personality assessments, is best measured by studying three factors: reliability, validity and utility.

Reliability of PPA

A test is said to be reliable if it provides the same score for each candidate on different occasions. Thomas International recommends that PPA be given at intervals of no less than 3 months.

The minimum satisfying figure for test reliability is 0.7 [8]. PPA consistently shows test/retest reliability. UK data is reviewed regularly.

Predictive Validity of PPA

Early data suggested that the PPA factors achieved predictive validities of up to 0.56 when employees who had been selected for employment using the PPA were rated on their job performance [9]

Other research by Professor Sidney Irvine focused on particular job roles for specific clients and the results were published in the journal “Current Psychology” [10] The research shows that the Thomas PPA gives good predictive validity when objective and verifiable criteria are used. It shows clearly distinguishable profiles for different job types and also differences within profiles for successes and failures in these jobs.

Construct Validity of PPA

Any test or behavioural assessment can be said to be valid if it measures what it claims to measure. Construct Validity is where test and retest trials using other instruments are conducted to confirm that PPA is saying similar things about the same people.

Studies conducted in the UK compare PPA with 16PF and OPQ factor 3 indicate this is the case. Between 1981 and 1987 major trials were conducted and these studies clearly show that the PPA dimensions of Dominance, Influence, Steadiness and Compliance are clearly recognisable when defined by the factor names of these instruments [11]


  1. Marston, W. M. (1928) Emotions of normal people. New York: Harcourt, Brace
  2. Gordon (1953), Denton (1954), LaForge (1955), Suczek (1955) and Clarke (1956
  3. Hendrickson, T. M. Personal Profile Analysis: a technical manual. Marlow: Thomas International Systems (Europe) Ltd
  4. Thomas International (1986b). TIRR-2 Descriptions of 4083 PPA results: Correlations and Distributions. (Cripps, B., and Geelhoed, E., Shailer, S., and Scott, C. Marlow: Thomas International Management Systems (Europe) ltd.
  5. Hendrickson, T. M. (undated). Personal Profile Analysis: a technical manual. Marlow: Thomas International Systems ( Europe) ltd
  6. Hendrickson, T. M. Personal Profile Analysis: a technical manual. Marlow: Thomas International Systems (Europe) Ltd
  7. Hendrickson, T. M. Personal Profile Analysis: a technical manual. Marlow: Thomas International Systems (Europe) Ltd
  8. Kline, P (1983). Personality: measurement and theory. London: Hutchinson.
  9. Thomas Technical Resource Book 2003 TIRR-6, pages 69-70, table 6.3
  10. Irvine, S. H., Mettam, D. & Syrad, T (1994). Valid and more valid? Keys to understanding personal appraisal processes at work. Current Psychology, 13, 27-59
  11. Irvine, S. H. 2003. Personal Profile Analysis - The Technical Resource Book
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