With over three decades of data taken from 470,846 participants and 355 academic journal articles, dissertations, manuscripts and technical manuals, scientists have made a pretty good case for men of all ages being significantly more likely than women to exhibit narcissistic tendencies. 

What does this mean? Well, it's not all bad, especially if you're an ambitious person, but narcissism isn't particularly great either, because it can make things pretty unpleasant for those around you. 

"Narcissism is associated with various interpersonal dysfunctions, including an inability to maintain healthy long-term relationships, unethical behaviour and aggression," lead researcher Emily Grijalva, from the University at Buffalo School of Management in the US, said in a press release. "At the same time, narcissism is shown to boost self-esteem, emotional stability and the tendency to emerge as a leader. By examining gender differences in narcissism, we may be able to explain gender disparities in these important outcomes."

In their meta-analysis, Grijalva's team looked at three different aspects of narcissism - leadership/authority, grandiose/exhibitionism and exploitative/entitlement - and studied the instances of these behaviours shown by the male and female participants across each one. They looked at US college student cohorts over time, from 1990 to 2013, and across different age groups. 

Gender difference effect sizes for three facets of narcissism were calculated by subtracting the mean for men from the mean for women, and dividing that by the pooled standard deviation to come up with 'd' as the quantifier. Based in these calculations, they found that by far, the widest gap between men and women was a feeling of entitlement (d = 29), which I'm guessing comes as a surprise to no woman anywhere. "This result suggests that compared with women, men are more likely to exploit others and to believe that they themselves are special and therefore entitled to privileges," the team wrote in the Psychological Bulletin. 

The second largest gap between the sexes was in the leadership/authority aspect of narcissism, which scored a d = 20. This means that compared to women, men were more likely to exhibit assertiveness, the motivation to lead, and a desire for more power over others, the researchers report.

But when it came to grandiose/exhibitionism aspect of narcism, the team found almost no difference between the sexes - d = 4. "In other words, both genders were almost equally likely to endorse characteristics consistent with vanity, exhibitionism, and self-absorption," the team writes.

Overall, they found a consistent gender difference in narcissism, with men scoring a quarter of a standard deviation higher in narcissism than the women (d = 26). They suggest that the differences between the behaviours displayed by the male and female participants could come from the way we tend to interpret gender stereotypes. "Individuals tend to observe and learn gender roles from a young age, and may face backlash for deviating from society's expectations," Grijalva said in the press release. "In particular, women often receive harsh criticism for being aggressive or authoritative, which creates pressure for women, more so than for men, to suppress displays of narcissistic behaviour."

Interestingly, when the researchers looked separately at vulnerable narcissism, which is another, less-studied form of narcissism characterised by low self-esteem, neuroticism, and introversion, they found no difference between the instances of women and men exhibiting this trait.

Now, before everyone starts getting upset about what these results could be saying, the researchers are the first to point to that while their results are pretty clear, they're not casting dispersions about every man, or every woman. They conclude in their paper:

"Narcissism is a trait with a relatively negative connotation. We must therefore emphasise that the gender differences referred to in this article do not apply to every individual within a group. Not all men are entitled or exploitative. Not all women are low in a sense of leadership and motivation for authority. 

The current results are consistent with the finding that within-group trait differences are generally larger than differences between gender groups. Although we are saying that the average man tends to be more narcissistic than the average woman, we are not making generalisations to specific individuals."

The researchers say that across the 31 years they examined, neither sex showed any signs of becoming more or less narcissistic over time, which means, no, the selfie explosion doesn't mean we're now more narcissistic than our parents. But if you do post a lot of selfies, you might want to check out this separate study, published last year, which linked both narcism and psychopathy to males who post a lot of selfies online.