Narcissism often gets a bad rap. Research has shown us that CEOs with too much ego underperform their peers during a tough economy, often take excessive risks and may be overpaid.

But research has also shown its positive side. Narcissistic CEOs are more likely to adopt disruptive technology, leading to greater innovation. Having narcissists on your team can equal more creativity. And putting a grandiose person in charge can also mean more charismatic leadership.

So which is it: good or bad? A new study published this month in the journal Personnel Psychology tried to answer that question, doing what academics call a "meta-analysis" of existing research on narcissism and organizational performance. The researchers aggregated the findings of more than 50 studies, including one that examined the connection between narcissism and the prominence of a CEO's photo in an annual report and one that looked at correlations between media praise for a CEO and corporate performance.

What they found was that narcissists are more likely to reach leadership positions, but there was no consensus answer for how much narcissism really affects a leader's success. Disappointed they had nothing to show for their analysis, the researchers decided to use data from H.R. consulting firm Hogan Assessment Systems to try to find out—if narcissism isn't categorically good or bad—whether a happy medium exists instead.

"I was surprised no one had ever checked," says Peter Harms, a management professor at the University of Nebraska at Lincoln and one of the study's co-authors. "There must be somewhere between a total lack of confidence and malignant self esteem," he says, that would be appropriate for good leadership.

As it turned out, they were right. By analyzing personality assessments and performance evaluations from six data sets, the researchers found that the relationship between narcissism and leadership effectiveness took on the shape of an upside-down U. The leadership ratings of those at the extremes (the insecure and the timid on one side, and the toxic self-aggrandizers on the other) were poor, while those in the middle did very well.

"The ancient Greeks were right," Harms says. "Everything in moderation."

Harms says that if companies choose to screen for narcissism in their hiring practices or personality assessments of leaders—say, not hiring or promoting anyone who rates in the top or bottom 10 percent—they should first do an internal evaluation of what an optimal level is for their organization. What rates as average levels of ego and confidence at a hospital, for instance, might be very different than at a Wall Street bank.

And then, of course, narcissism has to be taken in context. "A narcissist who's not very smart or hard-working is a disaster," Harms says. "But a narcissist who's really smart and really hard working could end up being someone brilliant like Steve Jobs."

Jena McGregor is a columnist for On Leadership.

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