People are claimed to belong to one of sixteen discrete personality types along four binary dimensions.
The instrument derives from Jung by way of two authors without training in psychometrics, and its central claim, that people fall into discrete types, fails on the data: the underlying traits are normally distributed, so dichotomising them assigns people near the middle almost at random. A substantial share of takers receive a different type on retest weeks later.
In practice
- An organisation that assigns roles by type has sorted its staff on a measurement that would change if repeated.
- A description that most people recognise themselves in is exhibiting the Barnum effect, not measuring them.
- Possible explanations
- One explanation for its durability is that the feedback is flattering and non-judgemental, so people accept it. Another is organisational: it gives teams a shared vocabulary without confronting anyone with a deficiency.
- In its favour
- The underlying dimensions overlap substantially with measured traits, particularly extraversion and openness, so the questionnaire is not measuring nothing.
- Against it
- Personality researchers reject the type claim: the dimensions are continuous rather than bimodal, so the cut points are arbitrary, test-retest reliability is poor enough that many people change type on retaking, and the types do not predict job performance.
- Standing
- Rejected by personality researchers. The dimensions are continuous rather than bimodal, so the cut points are arbitrary; test-retest reclassification rates are high; and the Big Five accounts for the same variance with better structure. Its commercial use is very large.
- Subject
- Psychology & Behavior
- Essay
- Theories of the mind, from the lab to the bookshop