# What would it mean for the Myers-Briggs personality test to be pseudoscientific?

I recently had a two day training course at work where they made a big fuss about Myers-Briggs personality tests, and ensuring that we learn to play to our strengths and identify weaknesses based on this test.

Looking it up after the course, I saw that [Wikipedia's view](https://en.wikipedia.org/wiki/Myers%E2%80%93Briggs_Type_Indicator) on it isn't particularly positive:

> The Myers–Briggs Type Indicator (MBTI) is a self-report questionnaire that makes pseudoscientific claims to categorize individuals into 16 distinct "personality types".

Now Wikipedia's probably right, and I've got better things to do than to dive into the research here. But I think possibly more important than whether or not the MBTI is pseudoscientific or not, is what would it mean for it to be pseudoscientific?

Once we make sure we're asking the right questions, we can then find the right answers. But if we're not asking the right questions, all our thinking on this is going to be confused.

A quick overview of the MBTI
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An MBTI test asks a bunch of questions, e.g. "what word do you prefer: 'planned' or 'spontaneous'?". It then scores the answers across 4 axes:

E  Extraversion-Introversion  I   
S           Sensing-Intuition        N   
T        Thinking-Feeling           F   
J      Judgement-Perception     P

Although you have a continuous score along each of these axes, it breaks them down into a binary choice based on a fixed threshold, to assign everybody to one of 16 buckets (e.g ENFJ).

It then provides descriptions of each of the 16 personality types, which are meant to be useful in helping yourself and others relate to you and how you think.

Each of these 4 axes, are broken down into 5 subaxes. E.g. the Extraversion-Introversion axes is broken down into:

Initiating–Receiving  
Expressive–Contained  
Gregarious–Intimate   
Active–Reflective   
Enthusiastic–Quiet

The total Extraversion-Introversion score is the average of these 5 factors.

Different ways for the MBTI to be more or less right/useful/accurate/scientific.
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**Retestability**

If you take the MBTI two days apart, how closely do your scores match each other? What if we give you an amnesiac after the first test, so you don't remember your answers, or you're feeling much happier/more excited/calmer/etc. the second time you take the test? What about 5 weeks apart, or 5 years apart?

If it takes very little to push scores apart then the MBTI is mostly a measure of your current mood/state of mind. If it stays consistent over long periods of time then it's more likely to be measuring something inherent to you.

Even if not inherent, the MBTI might still be useful as a measure of your current state of mind, or even that you have semi-consistent states of mind. For example, it could be that you're always an INTP after you finish playing tennis, and that provides a useful lens for anyone who wants to interact with you on a Wednesday morning.

Note it's possible that some axes/subaxes are retestable, and some aren't, in which case parts of the MBTI might be inherent, and others are not.

**How strongly do sub factors correlate with each other?**

If the 5 subfactors for Extraversion-Introversion correlate with each other strongly, then it's meaningful to combine them into a single factor. If not, then the MBTI might be measuring 20 different personality axes, but the 4 main ones should be ignored, as they don't usefully abstract away the underlying complexity. Since the MBTI is so focused on the 16 personality types, this would cast serious doubt on the ability of the MBTI to be a useful predictive tool.

**Is there any interesting structure in the distribution of scores across the 4 axes?**

Imagine you plot the scores for a large number of individuals in a 4 dimensional scatterplot. Does it just look like the scores are distributed fairly randomly across all 4 axis so that the combined scatter plot looks roughly like a 4-sphere, or does more interesting substructures appear - e.g. that we see dense clusters of points within each of the 16 buckets, and then sparse gaps between clusters.

If we see such interesting structure, that implies the MBTI is carving reality at the joints. People genuinely fall into one of 16 buckets, and the binary division of each axis is justified.

If not the MBTI might still be useful - we often arbitrarily divide continuous categories into discrete ones to make modelling the world simpler, and people who are close to each other on the scatterplot are still likely to be similar. But we have to recognise then that the MBTI is in the map, not the territory, and doesn't in any way correspond to some fundamental property about reality. It would be equally valid to carve each dimension into 3 categories, for a total of 81 personality types, and our choice to use 16 is just an attempt to get sufficient signal from the test whilst minimising complexity.

**Does the MBTI have predictive power?**

Imagine I tell three people to predict what a subject will do in a particular situation. I tell one of the people the correct MBTI for the subject, another an MBTI that is 50% correct, and the final one the opposite MBTI score.

Will the one with the correct score perform better than the other two? How much better? To the extent the MBTI has predictive power it's useful, and to the extent it doesn't it's pointless, even if it fails/passes all the other tests.

Conclusion
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I think this exercise is a useful one. Often people get into arguments about the validity of things without ever clarifying what they're actually arguing about, and so the argument goes round in circles.

By stopping and thinking about exactly what you're claiming, and what the alternatives are, it's much easier to have a productive discussion.

Now if somebody claims that the MBTI is pseudoscientific, or incredibly useful, you can go through each of these 4 tests, and see where you agree or disagree. Then you can research the ones you disagree about in more depth. This of course is not limited to the MBTI.