In the early 1970s, a team led by Carl Wordat Princeton University recruited white students for an experiment they weretold was about assessing the quality of job candidates. Unbeknown to them, theexperiment was really about how they treated the supposed job candidates, andwhether this was different based on whether they were white or black.

Despite believing their task was to findthe best candidate, the white recruits treated candidates differently based ontheir race – sitting further away from them, and displaying fewer signs ofengagement such as making eye-contact or leaning in during conversation.Follow-up work more recently has shown that this is still true, and that thesenonverbal signs of friendliness weren't related to their explicit attitudes, sooperate independently from the participants’avowed beliefsabout race and racism.

So far the the Princeton experimentprobably doesn't tell anyone who has been treated differently because of theirrace anything they didn't know from painful experience. The black candidates inthis experiment were treated less well than the white candidates, not just inthe nonverbal signals the interviewers gave off, but they were given 25% lesstime during the interviews on average as well. This alone would be aninjustice, but how big a disadvantage is it to be treated like this?

Word's second experiment gives us a handleon this. After collecting these measurements of nonverbal behaviour theresearch team recruited some new volunteers and trained them to react in themanner of the original experimental subjects. That is, they were trained totreat interview candidates as the original participants had treated whitecandidates: making eye contact, smiling, sitting closer, allowing them to speakfor longer. And they were also trained to produce the treatment the blackcandidates received: less eye contact, fewer smiles and so on. All candidateswere to be treated politely and fairly, with only the nonverbal cues varying.

Next, the researchers recruited more whitePrinceton undergraduates to play the role of job candidates, and they wererandomly assigned to be nonverbally treated like the white candidates in thefirst experiment, or like the black candidates.

The results allow us to see theself-fulfilling prophesy of discrimination. The candidates who received the"black" nonverbal signals delivered a worse interview performance, asrated by independent judges. They made far more speech errors, in the form of hesitations,stutters, mistakes and incomplete sentences, and they chose to sit further awayfrom the interviewer following a mid-interview interruption which caused themto retake their chairs.

It isn't hard to see that in awinner-takes-all situation like a job interview, such differences could beenough to lose you a job opportunity. What's remarkable is that theparticipants’ performance had been harmed by nonverbal differences of the kindthat many of us might produce without intending or realising. Furthermore, theeffect was seen in students from Princeton University, one of the world's eliteuniversities. If even a white, privileged elite suffer under this treatment wemight expect even larger effects for people who don't walk into high-pressuresituations with those advantages.

Experiments like these don't offer thewhole truth about discrimination. Problems like racism are patterned by so muchmore than individual attitudes, and often supported by explicit prejudice aswell as subtle prejudice. Racism will affect candidates before, during andafter job interviews in many more ways than I’ve described. Whatthis work does show is one way in which, even with good intentions, people'sreactions to minority groups can have powerful effects. Small differences canadd up.