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We Expect Too Much From Personality Tests

I've noticed an increased interest in the value of personality assessments in our work lately. What has stood out to me is the expectation for personality assessments to deliver more than the science can promise. Some of those expectations reflect cognitive errors in how we think about personality and behavior.


For the Skimmer:

  • Personality can predict how well someone will fit with a job, but not as accurately as most people would think

  • We are biased towards thinking our behavior reflects inherent qualities like personality rather than demands of situations and environments

  • We tend to categorize people into personality types, which is inaccurate and oversimple

Our brains can be pretty frugal. If there's a shortcut that will save our brains some energy, they'll usually take it. For example, you can probably think of a bunch of implications that don't need to be spelled out when you hear someone works in a tech job versus in a blue collar job. However, these mental shortcuts work less well to explain complicated things - like humans - where shortcuts risk becoming stereotypes rather than time-savers.

This same kind of mental frugality helps explain how people tend to misuse or misinterpret personality assessments. The popularity of assessments like the Myers-Briggs, CliftonStrengths, or the DISC encourage people to think of personality in terms categories or types, which can be a real oversimplification. Personality traits are similar to height or weight in that we all have them in degrees. When we describe a person as "tall," we mean to say that they are taller than the average person, but it would be really time-consuming to always articulate that.

The problem with using categories or types when talking about personality is that doing so implies everyone in the category is the same, which of course can't be accurate. This is why you might hear someone describe themselves as an "extroverted introvert," or as an "ambivert." That clunky language happens because people are more complicated than the categories into which we try to put them.

Even in my experience using more in-depth and comprehensive assessments, I've noticed some trends in how people think about personality:

  • We like hearing about ourselves because it gives us something to point to. Thanks to pretty charts and numbers, personality assessment results feel objective and definitive. They let us explain thoughts we've had, words we've said, and choices we've made.

  • Few people are surprised when I walk them through their personality assessment results. Some are more self-aware than others, but it's pretty rare (and sometimes difficult) when a person just doesn't see themselves in their results.

  • In some cases, knowledge of our personality can even let us feel vindicated, or free from responsibility: "I don't mean to be like that, it's just how I'm wired."


However, pretty much all these same things can be said about horoscopes and palm readings. Thanks to the human tendency to selectively pay attention to things that confirm our beliefs, and to ignore conflicting data, personality results (and horoscopes) can feel more accurate than they really are. Thus, it's easy for us to overinterpret personality data, and difficult for us to not overgeneralize the inferences we make from those data.

The tricky thing is, personality can predict how people will behave a lot of the time, just not all of the time, or even as often as we'd like to think. And our lazy brains have a really hard time handling that nuance when it comes to thinking about personality at work.

For instance, conscientiousness, a personality trait that describes a person's follow-through and responsibility, is a consistently strong predictor of job performance in most jobs. It makes sense that people who are more meticulous and diligent generally perform better at work than the rest of us. But even this trait, the most work-relevant aspect of our personalities, only explains about 3% of the variability in job performance.


Only about 3% of the variance in job performance is explained by conscientiousness.

The other 97% is accounted for by other characteristics of the person like their intelligence and experience, or more importantly, things not related to the person at all. Our personality describes how we tend to behave across situations, and especially when the situation doesn't dictate our behavior.

For example, if I interview someone who is really warm and bubbly in conversation with me, I might infer that they are usually a gregarious and warm person. Or, it could just as well be that person is responding to the social expectations of being in an interview. They might actually be more reserved than most people, but in that moment their behavior is influenced by clear expectations to be talkative.

A person's behavior at any given moment will always be the interaction of who they are and the situation they're in. That complexity is a challenge for our shortcut-loving brains to process. We'd much rather attribute someone’s behavior to who they are rather than where they are. Psychologists describe this tendency as the fundamental attribution error, and it's one of the reasons why people overvalue personality assessments.

We'd much rather attribute someone’s behavior to who they are rather than where they are.

Despite the challenges, measuring personality differences among people is still valuable and worth the effort to do it right. When used correctly, personality assessments can help guide hiring decisions and provide people with insightful feedback. But even the best assessment isn't a crystal ball and the importance of context can't be overstated.

Here are some other things to consider regarding the use of personality assessments:

  • We should pause before using a label or category to explain a person's behavior. Describing someone as "an introvert" or any other personality trait is an oversimplification.

  • Personality assessments are useful, but buyer beware: there's a lot of junk science out there. Tim Jackson wrote an excellent summary of this point here.

  • The culture of an organization and the demands of individual jobs have implications for what personality traits will serve people the best. In other words, context matters.

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