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So you're with your friends, trying to decide where to go for dinner. One says they want Chinese food, the other suggests Indian, and then they both offer to go to the other's chosen restaurant and it's been ten minutes and nobody's making a decision.

You finally jump in and say, “OK, let's just get Chinese,” and then one of them responds with, “Ugh, you're such a Type 8!” They're referring to one of the 9 personality types in what's known as the Enneagram system— specifically, the type that describes a challenger or protector. If they were trying to say you're controlling, that probably wasn't very nice. But it was also probably wrong, because despite its popularity, the Enneagram is one of those classification systems that doesn't have solid science to support it and isn't actually a good measure of personality.

You can learn a lot about psychology from how popular it is, though. The current form of the Enneagram, which started to become more well-known about 50 years ago, puts everyone in one of 9 categories. For example, you could be a Type 1, called either the Reformer or the Perfectionist depending on whom you ask.

Supposedly, Type 1s are committed to idealistic principles and tend toward perfectionism. Or you might be a Type 5, the Investigator or Observer—someone who's perceptive and intellectual. Or maybe you're a Type 8, the Challenger or Protector your friend mentioned, who takes charge and follows their instincts.

In the Enneagram, the 9 personality types are arranged into a circle. Each type is a point on the outside of the circle, and the points are connected by lines that represent how someone with a given personality type might act under different circumstances. For example, when you're stressed, you might be expected to take on some of the features of one of the types that's connected to yours.

The idea is that each person will have one type that fits them best. Supposedly they all have their own strengths and weaknesses. There's no best or worst type to have, and people are encouraged to try to become the best version of their personality type.

But you might have noticed that you can have a lot of these characteristics at the same time, even just among the three types I've mentioned so far. Like, I don't know about you, but I try to stick to my principles, and I also like thinking about things in an intellectual way, and when someone needs to take charge I have no problem filling that role as well. So there's a pretty fundamental flaw in the system—but we'll get to that.

First, the research:. There's not a ton of it, but the studies that have been done haven't found much evidence to support characterizing personalities this way, especially compared to other types of personality tests. One major drawback is that it's inconsistent.

You can end up with totally different results depending on the test you take. A few studies have found some links between Enneagram types and scores on the Big Five, the main measure of personality that's used in research because it's been shown to be both reliable and fairly accurate. But even those studies acknowledged that it's not the best way to go.

Either way, it might seem pretty weird that the Enneagram is so popular given how little research there is to support it. But its popularity actually makes sense from a psychological perspective. In fact, one of the reasons the Enneagram is so popular may also be its main flaw:.

Many of the personality types are relatable for almost everyone. Psychologists have found that we tend to agree with vague, general personality statements—for example, “You like being around others, but you value having personal time as well.” It's called the Barnum effect. We've known about it since at least 1949, and it's been the focus of lots of studies since.

Basically, the participants take a personality test, and you give everyone the same result regardless of how they answered. People tend to say that their result describes them well, even though it wasn't actually personalized based on how they answered the test questions. That's the problem with personality tests that rely on vague statements, like the Enneagram: the results may technically be true, but they aren't very informative because they're true for lots of people.

There's also a larger phenomenon that might be going on here: subjective validation, where something feels more true because it's personally meaningful to you. It's part of our basic human need to find meaning in things:. Sometimes, people can be so motivated to find meaning that they choose to believe something even when there's not really much data to support it.

Psychologists think subjective validation could be a big part of why people believe in pseudoscientific ideas in general. But in this case, at least, there's an easy alternative that does have real science to back it up: the Big Five. Its name comes from the fact that it characterizes your personality based on five different traits: extraversion, agreeableness, conscientiousness, neuroticism, and openness to experience.

So maybe that's something to explore with your friend the next time they point out your Type 8 tendencies. There's no guarantee they won't find other ways to insult you, but hey, at least the jibes will be more accurate. Thanks for watching this episode of SciShow Psych!

If you're interested in learning about other popular-but-not-very-scientific personality tests and what the Big Five does differently, you might want to check out our video about whether personality tests can mean anything at all. And don't forget to go to youtube.com/scishowpsych and subscribe! [OUTRO ♪].