A drive to better understand ourselves and the people around us has led to the creation of a thriving industry built around personality testing. What can a personality test tell us about who we are? Shankar Vedantam, host of Hidden Brain podcast and radio show, explores the science behind personality tests, and the industry built around them. 
STEVE INSKEEP, HOST: If anybody with Internet access eventually sees the offer click here and take an online personality test, they're not very scientific. But they can be fun. BuzzFeed had a quiz called Which "Star Wars" Villain are You? Well, some employers are using more rigorous personality tests. So what can they really reveal about the people who take them? Here's NPR's social science correspondent Shankar Vedantam.</s>SHANKAR VEDANTAM, BYLINE: It's one of the most famous scenes in the "Harry Potter" series. Two lines of kids newly arrived at the Hogwarts School of Witchcraft and Wizardry march into a glorious dining hall. Young students make their way to the front where a crumpled wizard's hat awaits them. It is The Sorting Hat. The hat peers into the minds of the youngsters. After judging their personality traits, it decides which house they'll belong to during their Hogwarts education - brave Gryffindor, gentle Hufflepuff, smart Ravenclaw or ambitious Slytherin.</s>LESLIE PHILLIPS: (As The Sorting Hat) But where to put you?</s>DANIEL RADCLIFFE: (As Harry Potter) Not Slytherin, not Slytherin.</s>LESLIE PHILLIPS: (As The Sorting Hate) Not Slytherin? Are you sure? You could be great, you know.</s>SHANKAR VEDANTAM, BYLINE: There's something deeply appealing about The Sorting Hat. It knows people better than they know themselves.</s>MAKAYLA: Hi, my name is Makayla Blackburne (ph). And the house I'm in is in Gryffindor.</s>SHANKAR VEDANTAM, BYLINE: I ran into 10-year-old Makayla and a group of her friends recently at PotterVerse, a "Harry Potter" convention in Baltimore.</s>SHANKAR VEDANTAM, BYLINE: And do you all know each other really well?</s>UNIDENTIFIED CHILDREN: Yeah.</s>SHANKAR VEDANTAM, BYLINE: OK, good. All right, so here's a little test that I want to do, OK? We're going to pick Makayla. And you're not going to say it, but the rest of your friends on the count of three are going to call out and say what house you think she should be in, not what she says she's in or what she wants to be in but based on what you know of her, what house you think she should be in, all right? On the count of three. Ready? One, two, three.</s>UNIDENTIFIED CHILDREN: Slytherin.</s>UNIDENTIFIED CHILD: Hufflepuff.</s>SHANKAR VEDANTAM, BYLINE: And what had you said?</s>MAKAYLA: I said I was in Gryffindor.</s>SHANKAR VEDANTAM, BYLINE: Wait, your friends got you completely wrong.</s>MAKAYLA: Well, I went to this camp and it sorted me into Slytherin. But I am sort of cunning so, yeah, they're right. And she's right as well 'cause I am sort of nice.</s>UNIDENTIFIED CHILD: Yes, you are loyal to your friends, I would think.</s>SHANKAR VEDANTAM, BYLINE: Even among these young girls, it's easy to see how the question - what house are you in? - flows into a larger question. What kind of a person are you? This need to understand ourselves has fostered a thriving industry built on the marketing and sale of personality tests. Some categorize you by your favorite color.</s>SHANKAR VEDANTAM, BYLINE: UNIDENTIFIED WOMAN #1: And today you'll discover your true colors, the unique combination of traits that make up your personality.</s>SHANKAR VEDANTAM, BYLINE: Others promise that discovering your true personality will guide you to love.</s>UNIDENTIFIED MAN: Ever hear of the term hopeless romantic? Ever wonder if it happens to describe you? Well, welcome to ItsAllViral. And today, we're going to be seeing if you are indeed a hopeless romantic.</s>SHANKAR VEDANTAM, BYLINE: The most famous of these tests is the Myers-Briggs Type Indicator or NBTI. It sorts people into 16 personality types, each of which describes a way of seeing or dealing with the world. For example, if you're an ENFP, that means you're an extrovert, rather than an introvert, you rely on intuition more than facts, you're emotional rather than cerebral and you prefer to go with the flow rather than have a highly structured life. When Adam Grant, a psychology professor at the University of Pennsylvania first took the test, he found he was an INTJ, an introvert, an intuitor, a thinker and a judger.</s>SHANKAR VEDANTAM, BYLINE: But then a few months later, he took the test again.</s>ADAM GRANT: I got opposite scores on every dimension. I scored (laughter) now I was ESFP.</s>SHANKAR VEDANTAM, BYLINE: Grant says he began to question the reliability and validity of the test.</s>ADAM GRANT: It falls well short of most conventional reliability standards. And the Myers–Briggs proponents themselves will tell you that it doesn't predict anything.</s>SHANKAR VEDANTAM, BYLINE: Many personality researchers put greater stock in a test known as the Big Five. Grant says the Big Five has lots of peer reviewed data to back it up.</s>ADAM GRANT: We can predict your job performance, your effectiveness in a team with different collaborators, your likelihood of sticking around in a job versus leaving as well as your probability of your marriage surviving, depending on the personality fit between you and your spouse.</s>SHANKAR VEDANTAM, BYLINE: Allen Hammer, a psychologist and former chair of the Myers-Briggs Foundation, disagrees with Adam. He says the Myers-Briggs is as reliable as other personality tests and that it can predict real world outcomes.</s>ALLEN HAMMER: When people matched roommates on their psychological type, they got a 65 percent decrease in requests for roommate changes.</s>SHANKAR VEDANTAM, BYLINE: The origin story of the Myers-Briggs is unconventional. In the 1940s, an American woman named Isabel Myers became interested in the ideas of Carl Jung, a contemporary of Sigmund Freud.</s>ALLEN HAMMER: Her mother, actually, was interested in Jung first. And then Isabel, who was a housewife at the time and a writer, she got interested in type and then started looking at applications particularly around careers.</s>SHANKAR VEDANTAM, BYLINE: Isabel Myers and her mother, Katharine Cook Briggs, turned Jung's theories into a test. Myers also added her own ideas.</s>ALLEN HAMMER: Isabel Myers added a fourth dimension, and that's represented by the letters J and P.</s>SHANKAR VEDANTAM, BYLINE: Hammer does agree with Grant on one thing. He says the test should never be the only factor in hiring or promoting someone.</s>JESSICA COMSTOCK: By a show of hands or wands, how many people are familiar with the Myers-Briggs Type Indicator?</s>SHANKAR VEDANTAM, BYLINE: Back at the "Harry Potter" conference, I stopped by a panel discussion called Hogwarts Houses as Personality Types. The panel leader, Jessica Comstock, has designed a detailed chart to show how closely Hogwarts Houses align with Myers-Briggs categories.</s>JESSICA COMSTOCK: I'm going to do a little experiment with the first few people. So what is your MBTI?</s>JESSICA COMSTOCK: UNIDENTIFIED WOMAN #2: ISTP.</s>SHANKAR VEDANTAM, BYLINE: Comstock looked at her chart. ISTP matches to Slytherin.</s>JESSICA COMSTOCK: What is your house?</s>JESSICA COMSTOCK: UNIDENTIFIED WOMAN #2: Slytherin.</s>JESSICA COMSTOCK: Yes, it is.</s>SHANKAR VEDANTAM, BYLINE: The delight on the faces of audience members was palpable.</s>SHANKAR VEDANTAM, BYLINE: UNIDENTIFIED WOMAN #3: ESFJ.</s>JESSICA COMSTOCK: You said ESFJ. You're a Hufflepuff.</s>SHANKAR VEDANTAM, BYLINE: And as I looked out at the crowd in this packed conference room, I was struck by another idea. If "Harry Potter" houses work about as well as a psychological test being used by many companies to hire and fire people, well, it makes me want to pick up my wand and say, obliviate (ph). Shankar Vedantam, NPR News.</s>STEVE INSKEEP, HOST: Shankar's the host of the Hidden Brain podcast and radio show. And later this afternoon, on All Things Considered, he's going to look at how the labels we put on each other can shape who we become.