The Myers-Briggs Type Indicator is probably the most widely used personality test in the world.
An estimated 2 million people take it annually, at the behest of corporate HR departments, colleges, and even government agencies. The company that makes and markets the test makes somewhere around $20 million each year.
The only problem? The test is completely meaningless.
"There's just no evidence behind it," says Adam Grant, an organizational psychologist at the University of Pennsylvania who's written about the shortcomings of the Myers-Briggs previously. "The characteristics measured by the test have almost no predictive power on how happy you'll be in a situation, how you'll perform at your job, or how happy you'll be in your marriage."
The test claims that, based on 93 questions, it can group all the people of the world into 16 different discrete "types" — and in doing so, serve as "a powerful framework for building better relationships, driving positive change, harnessing innovation, and achieving excellence." Most of the faithful think of it primarily as a tool for telling you your proper career choice.
But the test was developed in the 1940s based off the untested theories of an outdated analytical psychologist named Carl Jung, and is now thoroughly disregarded by the psychology community. Even Jung warned that his personality "types" were just rough tendencies he'd observed, rather than strict classifications. Several analyses have shown the test is totally ineffective at predicting people's success in various jobs, and that about half of the people who take it twice get different results each time.