When was the last time you discovered a workplace problem thanks to your "open door policy"? Does "never" sound about right? Don't feel bad. You're not alone. Most employees just don't feel comfortable telling their boss about an abusive manager or how the project your team is working on is misguided.

According to a recent study, employees are holding back important information, information that could help your business run better, faster, more efficiently and more profitably. 

James Detert, professor of management at Cornell University's Samuel Curtis Johnson Graduate School of Management, and Ethan Burris, associate professor of management at the McCombs School of Business at the University of Texas at Austin, write in Harvard Business Review Magazine about their studies on the correlation between employees being able to speak honestly and company performance.

Detert and Burris found that companies where employees can freely voice their concerns and insights enjoy better over all performance and higher retention rates.

A national restaurant chain, Detert and Burris found, reduced turnover by 32 percent and saved $1.6 million a year after managers spoke honestly to their executives about concerns.

But getting people to talk openly is difficult. The researchers found that two main reasons are holding your employees back: A fear of consequences, including alienation, being skipped over for promotions, or getting fired, and "a sense of futility," they write.

Once you know your employees are scared to speak their mind or feel it's a waste of their time and effort, you can address these problems and start to foster a culture where people do speak up. Follow these tips to get your employees talking: 

Make feedback casual

Anonymous feedback and surveys will only perpetuate the idea that employees can get fired for blowing the whistle or sharing their suggestions to improve a project or aspect of the business. Detert and Burris found that if you make feedback and input a frequent, casual, face-to-face conversation, "idea sharing will feel less ominous and more natural," they write.

What you ask for is what you get

You don't get what you don't ask for. If you want feedback, you need to ask for it. The results might surprise you, Detert and Burris found that employees will speak up twice as much if a boss asks them to. Soliciting feedback informally can be much more effective than just being open to it when it comes your way.

Reverse the power structure

A boss's office is intimidating to an employee and intimidation doesn't exactly illicit honest feedback. Detert and Burris found that if you "soften power cues" you might help make employees more comfortable. Hold feedback sessions in a neutral room or a cafe. If they need to be in your office, set up a table and two chairs that are the same, lessening the power structure between the two of you.

"If you really want to get the truth from below, play down your power when interacting with employees," they write. 

Be an advocate

If you do not stand up for your employees when it matters, none of these changes will work. In a study of a restaurant and its employees, the duo found that the employees whose bosses advocated for them had "significantly reduced feelings of futility" and shared their ideas with their bosses 10 percent more than employees whose bosses didn't stand up for them.