When you’re hiring staff, how quickly do you make up your mind? Are you one of those managers who prides themselves on knowing the minute someone steps through the door whether they’re right for you? You get that ‘gut feeling’, you just know?

Well here are some scientifically-grounded reasons why you might want to rethink your reliance on gut feeling.

We all make judgements about people all the time. It’s human nature. We form impressions based on how someone looks and moves and speaks, on their clothes, their accent – and that’s before we take any account at all of what they actually say or do.

Some of these impressions are obvious – he’s wearing an expensive suit and driving Jag, he’s a successful businessman; she’s got a little bit of dried food on the shoulder of her jacket, she’s got a baby at home and came out in a hurry.

Some judgements we can articulate a bit, but they’re only half-formed. She’s called Bianca, she’s bubbly and blonde, giggles a lot and her skirt is a little bit too short – what impression are you forming about her IQ? He’s called Hugo Smythers-Cadwallader, he speaks awfully nicely and seems to ooze confidence – have you already decided whether you could work with him? So far, you don’t know much about these people, but it’s easy to see how in a selection situation, you (like everyone else) might struggle to see past your own stereotypes of them.

The judgements to really look out for, though, are the ones you don’t even know you’re making. Maybe you just have a hunch that this person will be brilliant for the job. You can’t put your finger on it. It just feels right. But supposing it’s because some small mannerism of theirs reminds you of that amazing boss you had in 1997? In reality, they may have none of the positive qualities your boss had, but your brain will fill in the gaps so you think they do. And it’s even worse, if they remind you of yourself.

When you’re hiring people, your job is to make judgements about them. You just need to make sure those judgements are based on sound criteria. And in a selection situation, gut feeling may be nothing more than a series of impressions, formed by your unconscious, that you can’t quite articulate.

If you want evidence of how misleading unconscious impressions can be, take a look at some of these experiments:

First of all there’s straightforward prejudice. You’d think we’d be past all this by now, but no. In an experiment that is deeply depressing in the 21^st century, groups of physics students were shown a video of a lecture by a physics professor and asked to assess the professor’s level of knowledge. The twist was that they were watching actors, all delivering exactly the same script, but sometimes the actor was male and sometimes female. And guess what? The men were judged to be more knowledgeable and to have a better grasp of the subject than the women. And what’s even sadder, is that female students made the same judgements, though not quite so strongly.

So if you’re interviewing a woman for a traditionally male role (or vice versa), chances are you have to overcome some part of your unconscious saying “Does not compute. Something wrong here”. Incidentally, if you think somehow you’re different, more enlightened, a true believer in equal opportunity and this doesn’t apply to you, have a go at Harvard University’s Implicit Association Test and discover your own unconscious biases around gender, race, age, obesity and so on. Trust me, we all have them.

Next up are those individual differences between people,  that you know, really, have nothing to do with how well a person can do a job, but they colour your view anyway. Take accent. Experiments have shown that a person’s accent can affect our perceptions of their intelligence – better to say nothing than speak with a Birmingham accent, apparently. Listening to someone with a foreign accent is harder work for our brains, with the knock on effect that we find what they say less credible, compared with someone with a local accent saying exactly the same thing. So when interviewing, it becomes incredibly important to listen to what people actually say, rather than the way that they say it.

There is also a mass of evidence showing that better looking people are judged to be better in many other ways – more sociable, more successful, more competent. Good looking candidates have an advantage when applying for jobs, though this may not apply to women applying for traditionally male jobs. Beautiful women are apparently too feminine to drive a truck or, heaven forbid, manage the finance department.

And what about clothing? In an ingenious experiment, female violinists filmed wearing concert dresses were judged, by professional musicians, to have played more proficiently than those wearing jeans or nightclub outfits, even though the soundtrack was actually identical in all cases.  People who really know how to grade musical performance heard differences which weren’t there.  Of course, they were primed to look for differences – they were led to believe they were hearing different people playing. But their brains hooked on to the cues provided by clothing to differentiate between people and turned those into (incorrect) judgements about performance.

You might make a (not unreasonable) negative judgement about a candidate who dresses inappropriately for an interview. But ask yourself this: which is easier to change – someone’s wardrobe or their basic skill set?

So far, we’ve looked at making erroneous judgements about people based on something to do with them – gender, accent, clothing, attractiveness and so on. Deep down, we probably all know we do this to some extent. The really surprising thing is how easily our brains are fooled by cues in the environment that have nothing to do with the person at all. Weirdly, our subconscious seems to work on metaphors. So, for example, you are more likely to judge someone as being a ‘warm’ person if you are holding a hot drink, rather than a cold drink. You tend to judge a candidateas more serious if you are holding a heavy clipboard with their CV on it – that perception of ‘weightiness’ has to be coming from somewhere and your brain is busy focusing on the candidate, so that’s where it attributes it.  Incidentally, the same research found that you should never try to drive a hard bargain while sitting in a soft chair.

Given how flawed our impressions of people can be, it’s hardly surprising that the traditional, unstructured job interview is consistently shown to be one of the least reliable methods of selecting someone for a job.  There are many more reliable methods you could be using, from simple aptitude tests, through in-depth psychological profiling to full-blown assessment centres, where candidates have the opportunity to demonstrate a range of skills in a mock-up of a working environment.

But if you’re going to use an interview, at least accept that first impressions are just that – impressions, not the full picture, probably not accurate. Don’t let your mind join the dots to create the picture you’re expecting to see. And that feeling in your gut? Well that might just be indigestion.