Not the look of a successful nonprofit CEO, according to a new study. (iStock photo)

They say you can't judge a book by its cover. But you can apparently conclude something about a CEO's performance by his or her facial features.

Past research has shown that CEOs who have physical characteristics associated with power or dominance -- things like a big mouth or a more widely shaped face -- have been linked with better performing companies. Yet a new study shows that when it comes to chief executives of nonprofit organizations, the opposite appears to be true: Those who appear less powerful to people actually tend to have more success.

For the study, recently published online in the journal Perception, two University of Toronto researchers asked people to rate photos of the faces of 100 top nonprofit CEOs -- all white and male to keep things consistent -- on four dimensions: Dominance, likability, trustworthiness and maturity, or how baby-faced their features appear. It then grouped dominance and maturity together to create a "power" score for each CEO and combined the other two traits to judge a CEO's "warmth." Separately, it asked another group of participants to judge how well they thought the men in the photos would be at leadership, based on appearance alone.

The researchers then compared their respondents' ratings to calculations in a Forbes magazine ranking of metrics such as each nonprofit's fundraising efficiency (how much private support is left after expenses) and charitable commitment (services offered as a percent of total expenses). In no case were respondents told the people in the photos were actually nonprofit CEOs.

What they found: Unlike past research linking dominance and the performance for-profit CEOs, nonprofit leaders with the highest "power" ratings were actually linked with less success. In other words, those who looked more likable or trustworthy performed better on the nonprofit metrics. The more powerful looking CEOs had significantly lower "charitable commitment" scores and marginally lower scores on fundraising efficiency and the total funds donated to charity. Those with the highest ratings for "leadership" also fared more poorly on the metrics, as well as on things like total revenue and total expenses.

What's happening here? "Among for-profit organizations, people who look more dominant are doing worse," said one of the co-authors, University of Toronto associate professor Nicholas Rule, in an interview. In the business world, people who are viewed as aggressive or assertive are linked with success, while in the nonprofit world, those thought to be good at building relationships appear to be viewed as having the upper hand. If their faces seem more approachable, Rule says, "that's possibly going to make them seem like a more trustworthy investment. If they're extremely dominant or evil looking, you're not going to want to donate them money" as much.

It's not that nonprofit boards are necessarily picking CEOs who look nicer, Rule says, but that those who have a more likable or trustworthy appearance could advance more easily -- whether through promotions based on perceived skills or through better actual performance, driven in part by donors' or outsiders' perceptions. "It's the fit argument," he says. "If someone looks the part, they're going to have advantages, and this can start extremely early. "

Rule is careful to note that there are always exceptions, and say he does not think nonprofit boards of directors should start selecting new leaders on the basis of how nice they seem. Instead, they should be aware of the potential for bias so they can avoiding missing people whose talents might be overlooked. "Visual impressions are extremely strong," he says. "Even when we know better that impression continues to reassert itself, we can be really easily swayed by the way people look."

He also says his study is a reminder that our definition of leadership should depend on the leader in question. In another part of the study, he asked respondents to rate how well they thought the men in each photo would do at leading a nonprofit organization, thereby positioning the CEOs in the right context. When they posed the question that way, people were more likely to give higher ratings to those CEOs in the study who had higher "warmth" ratings than they did in the first part of the study.

While Rule's past research in business, law and U.S. politics have shown a link between dominant appearances and perceived leadership, there is at least one other place where leaders who exude warmth do better: some Asian cultures. "In a study we did looking at electoral outcomes in Japan, we find that warmth is actually what predicts success rather than power," he said, noting that it makes sense given the collectivist culture in the region. "Our default, when we think about leadership, is to think about dominance. But when you ask people to consider the context, they make a change."

Read also:

CEOs with daughters run more socially responsible companies

What a boss sounds like

Like On Leadership? Follow us on Facebook and Twitter, and subscribe to our podcast on iTunes.