This article was originally published by The Business Journals.

Your unconscious mind is a speed demon. Research shows that people often form a first impression in a tenth of a second — and then stick to it.

This makes any hiring decision a treacherous tightrope act. In order to stay rational, you must give your conscious mind a chance to weigh in on the hiring decision, while preventing your quick-to-judge unconscious mind from forming a baseless opinion. Unwittingly, far too many hiring managers fall from the tightrope and base their hiring decision on style rather than substance.

Some scholars and lawyers now argue that looks are the last bastion of legal discrimination. And like every form of discrimination, “appearance discrimination” or “lookism” has nothing to do with competence or ability — yet the unconscious mind often has a hard time reconciling that distinction.

Why do we tend to hire tall CEOs?

Looks have a dramatic effect on some people’s careers. Author Malcolm Gladwell wrote in his book Blink that, on average, Fortune 500 CEOs are just a shade less than six feet. Given that the average American male is 5’9″, this means that CEOs as a group have about three inches on the rest of their gender.

Even more strikingly, in the general American population, 3.9 percent of adult men are 6’2″ or taller. Among Gladwell’s CEO sample, 30 percent were 6’2″ or taller.

Height obviously isn’t the reason for competence, but why is it such an overwhelmingly powerful factor? Gladwell writes, “Is this a deliberate prejudice? Of course not…Most of us, in ways that we are not entirely aware of, automatically associate leadership ability with imposing physical stature.”

And this tendency to stereotype extends beyond height. In the face of an attractive person, there’s a risk that you will see competence where it doesn’t exist. Likewise, you may unknowingly overlook the greater competence found in a less attractive person.

How to prevent appearance discrimination in your hiring

To successfully fill your organization with top performers, you need to reduce the risk that any factors other than competence enter into your hiring decision.

Here’s what works for my firm. Instead of forming our first impressions face to face, we start with a lengthy phone call. Properly structured telephone interviews let you focus on the most important factors of job performance without being distracted by appearance. Therefore, your first impressions are formed based on what a candidate has achieved, not how they look. And yes, we also try to avoid judging their voice too much.

By learning about someone’s accomplishments before you’ve met face-to-face, you give your rational mind a running head start. And this interview process also makes you less susceptible to the charms of someone confident, polished, and completely ineffective — the empty suits that wander the halls of so many executive suites.

As Gladwell puts it:

“Have you ever wondered why so many mediocrities find their way into positions of authority in companies and organizations? It’s because when it comes to even the most important positions, we think that our selection decisions are a good deal more rational than they actually are. We see a tall person, and we swoon.”