If you want to know if someone is a narcissist, just ask. It's that simple.

Researchers found they could reliably identify narcissistic people by asking one question, including the note you see at the end:

“To what extent do you agree with this statement: “I am a ‘narcissist.’ (Note: The word ‘narcissist’ means egotistical, self-focused, and vain.)”

Study participants rated themselves on a scale of 1 (not very true of me) to 7 (very true of me). The measure was tested and validated in a series of 11 experiments involving more than 2,200 people of all ages.

People who scored higher on narcissism on the SINS reported more positive feelings, more extraversion, and marginally less depression. But they also reported less agreeableness, and more anger, shame, guilt, and fear.

Results lined up very closely with several other validated measures of narcissism, including the Narcissistic Personality Inventory (NPI), a measure in wide use among clinicians. But the NPI has 40 questions to answer; the new survey, called the Single Item Narcissism Scale (SINS) — has one.

“People who are willing to admit they are more narcissistic than others probably actually are more narcissistic, ” said Brad Bushman, one of the co-authors of the study.

“People who are narcissists are almost proud of the fact. You can ask them directly because they don't see narcissism as a negative quality — they believe they are superior to other people and are fine with saying that publicly,” Bushman, a professor at The Ohio State University, said.

If someone thinks he or she is so great, why should we care? Narcissists can be found in our prisons, performing onstage and in sport arenas, working on films and artworks and in executive suites and boardrooms.

According to co-author Sara Konrath of Indiana University, understanding narcissism has many implications for society. “For example, narcissistic people have low empathy, and empathy is one key motivator of philanthropic behavior such as donating money or time to organizations.”

“Those who think they are already great don't try to improve themselves.” Bushman added. “And narcissism is bad for society because people who are only thinking of themselves and their own interests are less helpful to others.”

Bushman indicated that people who scored higher on narcissism on the SINS had both positive and negative outcomes. They reported more positive feelings, more extraversion, and marginally less depression.

But they also reported less agreeableness, and more anger, shame, guilt, and fear. And people scoring high on SINS also showed negative interpersonal outcomes, such as having poor relationships with others and less prosocial behavior when their ego was threatened.

The value of SINS is probably not as a replacement for longer narcissism questionnaires. The NPI and other instruments can provide more information to researchers, such as which form of narcissism someone has. But SINS offers a quick snapshot of narcissistic tendencies, particularly to researchers who are asking study participants to complete several different survey instruments and answer a long list of other questions, said Bushman.

You can take the test here. The study is published in PLOS ONE.