By Lucy Wilkins BBC News

Can a five-minute online test help tell whether you are racist or not? In the US, two million people have taken one and now a UK version is available.

Racism is a reality encountered every day in Britain, but how many people actually consider themselves racist?

It's difficult to be sure because people's true feelings are inevitably concealed by their politeness. So much so that those who harbour prejudice sometimes cannot admit it even to themselves.

But a five-minute online test (see Internet links, right), devised by American academics and newly launched in Britain, promises to strip away the veneer of respectability many people hold on to, and plunder the prejudices we harbour in the unconscious. The result - a truer picture of one's attitudes.

At least, that's the claim of those who drew up the Implicit Association Test. It works like this:

• Users put positive and negative words, such as "failure", "glorious", "wonderful" and "nasty" into categories of "good" and "bad", then do the same with images of black and white faces.
• By responding to the prompts as quickly as possible, the test aims to side-step what's known as "cognitive control" - the brief, but significant, time lapse we need to give an "acceptable" answer rather than a truly honest one.
• Depending on the magnitude of the result, respondents are judged to have either "little or no bias" or a bias rated as "slight", "moderate" or "strong".

The model can be applied far wider than race, detecting innate preferences for straight people over gay, thin over fat, even Harry Potter over Lord of the Rings.

But in the US its application as a test for racism has proved most controversial. Now the academics behind it have tailored a version for the UK, which juxtaposes good and bad words with white British names and Asian British names.

Most people have a preference for white faces rather than black, researchers say

The test is being is used to promote the London stage debut of A Patch of Blue, a classic American film of the 1960s about a blind white woman who falls in love with a black man.

About 25,000 people in the UK have completed the test, since it launched here six months ago. Like Professor Brian Nosek, many have found it suggests uncomfortable truths about themselves.

"I did the race test, and despite my egalitarian views and belief that I treated everybody equally, I had a much harder time putting the black faces with good than putting the white faces with good," says Prof Nosek, of the University of Virginia.

"That fact was so stunning that I began to wonder if I was lying to myself, was I lying to others? It was a humbling experience, and motivated me to assess my own attitudes."

With fellow psychologists Tony Greenwald from the University of Washington and Mahzarin Banaji at Harvard University, he developed the tests and put them online in 1998. Since then some two million people have taken them.

"People have engaged with it, whether they agree with it or not. It's starting conversation about the implications of their beliefs," says Prof Nosek. "We're giving people a sense that there may be a bias and giving them the chance to debate it."

"It certainly gave me pause to think about why I have reactions to people, the cause of which was not immediately obvious."

Warning to participants

The UK site is one of five international sites, with South Africa, Australia, Canada and India.

The test relies on quick reactions by those taking part

The Project Implicit website warns participants before they begin that they might not agree with the outcome: "If you are unprepared to encounter interpretations that you might find objectionable, please do not proceed further."

Katy - not her real name - who is 23 and lives in London, says it provoked some difficult questions.

"I never classified myself as having any racist feelings. I've always though I was liberal and open-minded. But the test told me I had a moderate bias in favour of white Britons," she says.

"At first I thought it was wrong, but then I began to think it could be telling me something about myself I don't want to admit to. It's quite depressing."

But not everyone is convinced. Some critics argue it has more to do with hand-eye co-ordination and manual dexterity than unearthing deep-seated prejudices. Others are sceptical such a test can determine whether someone is actually a racist. Clinical psychologist Nick Banks says psychometric tests - tests that measure personality - need a validity stamp to show they have been tested.

"I don't see it on this test and I suspect they're trialling it on the internet to get the verification."

Death threats

He calls the test "crude" for dividing opinions into "good" and "bad". "It's called dichotomous thinking. Most things in life are more complicated. Good tests allow you to grade your response on a scale of one to five or more," says Dr Banks.

"It depends what this test is for. If it's there to provoke debate about racism, that's ok. But if it's going to be used in a selection process for a job, then it's too blunt."

Others have taken greater offence, says Prof Nosek, with some going so far as to send death threats to him and his colleagues.

"But that scepticism is also important. Science needs to be put to the test, and not just by people, but by scientists as well," he says.

He said there are about 200 virtual labs around the world which are using similar online tools for studying.