You need to hire the best possible employees. You need to hire superstars.

But superstars have options. For talented people, the job market is a seller's market: Because they're in demand they can to a large extent choose where they want to work.

That's at least partly why recent research by Glassdoor -- involving nearly 100,000 interview reviews and offer decisions -- shows that last year over 17 percent of job offers were rejected by candidates.

Yep: Nearly 1 in 6 were offered a job they decided to turn down.

So how can you increase the odds that great candidates will accept your job offer?

Make the job interview more difficult.

According to Glassdoor, the acceptance rate for people between 25 and 34 increased by 3 percentage points when the interview process was more "difficult." And candidates in professional and technical fields are most likely to accept an offer if their interview is "difficult" (more on the rating scale in a second.)

One reason? For the candidate, the interview is a good way to gauge the potential of a particular employer or job. "If the interview process is tough," the thinking seems to go, "then that means getting a job here is tough -- which means getting in the door should be great for my career."

According to Daniel Zhao, co-author of the survey:

Research clearly shows the interview has a huge effect on how candidates see you as a company. Skills and career development are a priority for younger workers, and interviews are an opportunity for them to see if the company they're applying for will equip them with the experience they want.

Of course you might think your interview process is already tough. 

Think again. Glassdoor used a scale of 1 to 5, with 1 being "easy" and 5 being "very difficult." Only 10 percent of interviews were ranked as a 4, or "difficult."  And only 1 percent were considered "very difficult."

Which means the odds are candidates feel your interviews are easier than you think.

Which means making your interviews harder should pay off: Increasing the interview difficult by one level increases acceptance rates by nearly 3 percentage points.

Tests Work -- As Long As They're Skills Tests

Aside from asking more difficult interview questions (here are a number of interview question options), one way to increase the difficulty of the interview process is to have candidates complete some form of testing.

Skills tests, though -- not personality tests. Taking personality tests actually lowered acceptance rates by over 2 percentage points.

Maybe that's because superstars want to work for people who care more about results than personality: Taking applicable skills tests increased acceptance rates by over 2 percent.

And As Long As They Don't Involve Brain Teasers

Many people feel having to answer a brain teaser question during a job interview feels like a (jerk) move, and science backs up their intuition. 

How you answer a brain teaser says almost nothing about how you will perform on the job, but it says a lot -- and none of it good -- about the interviewer who enjoys asking the question.

Brain teaser interview questions are an example of aggressive interviewer behavior that lacks evidence for validity and is unsettling to job applicants... narcissism and sadism explain the likelihood of using brainteasers in an interview.

Yep: Jerk move. 

All brain teasers reveal is that the interviewer enjoys putting people on the spot and watching them squirm. Which is the last thing any interviewer should want to do -- especially since great candidates -- candidates with options -- will see that as reason enough to turn down a job offer.

Instead, do this. First, establish a consistent rubric for how you assess candidates.

Then use behavioral interview questions to not only determine how candidates have performed in real-world situations but to also get a sense of what they consider to be "difficult."

The answer to, "Tell me about the toughest decision you've had to make in the last six months" instantly gives you a sense of what the candidate considers to be a "tough" decision. 

Then consider adding a skills test to the process. (Tests are available for just about every job and industry; just make sure you administer the tests consistently, and that every short-list candidate takes the test. Where hiring processes are concerned, consistency -- and fairness -- is everything.)

And then ramp up the difficulty, because the research shows many candidates -- especially the great ones -- won't think your process is as tough as you do. They'll know, within minutes, if your process is easy, or difficult, or very difficult.

The answer to that question plays a significant role in how likely they are to accept your job offer.

Which means increasing the difficulty of your interviews will not only help you better evaluate candidates... it will also make it more likely that a superstar will say, "Yes."