A new study has revealed an incredibly simple way to identify a narcissist – just ask them.

A series of 11 experiments covering more than 2,200 people of all ages has shown that most narcissistic people will reveal themselves after a single question.

Researchers are calling it the Single Item Narcissism Scale (SINS).

The new test has one question;

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

Participants rated themselves on a scale of 1 (not very true of me) to 7 (very true of me), and researchers then compared those figures against other validated measures of narcissism, including the widely used Narcissistic Personality Inventory (NPI).

But what the NPI uses 40 questions to answer, the SINS test gets from one.

“People who are willing to admit they are more narcissistic than others probably actually are more narcissistic,” said Brad Bushman, professor of communication and psychology at Ohio State University and co-author 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.”

Understanding narcissism has a number of implications that could help close some gaps in 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,” Bushman said.

“Overall, narcissism is problematic for both individuals and society. Those who think they are already great don't try to improve themselves

“And narcissism is bad for society because people who are only thinking of themselves and their own interests are less helpful to others.”

The researchers say SINS should not replace longer narcissism questionnaires, such as the NPI and other instruments.

These deeper probes can provide more information to researchers, on the form and style of a person’s narcissistic tendencies.

“But our single-item scale can be useful for long surveys in which researchers are concerned about people getting fatigued or distracted while answering questions and possibly even dropping out before they are done,” Bushman said.

The difference between the 20 seconds it takes to answer in the SINS measure against the 13.3 minutes to answer the NPI could have a big impact on studies which require multiple instrument and lists of other questions.

“We don't think SINS is a replacement for other narcissism inventories in all situations, but it has a time and place,” Bushman said.

One experiment found SINS was positively related to each of the seven subscales of the NPI (vanity, exhibitionism, exploitativeness, authority, superiority, self-sufficiency and entitlement), another found that participants had similar scores on SINS when tested 11 days apart, while a third experiment replicated past work to show that people who scored high in narcissism were more likely to engage in risky sexual behaviours. It also showed narcissists had difficulty maintaining long-term committed romantic relationships.

People with a higher narcissism score on the SINS test reported more positive feelings, more extraversion and marginally less depression. However, they also reported less agreeableness, and more anger, shame, guilt and fear.

High-scoring SINS narcissists reported feeling less sociable when their ego was threatened.

The study is published in PLOS One.