People's racial prejudices are influenced by where they live, reports a new study led by Oxford University psychologists.

The researchers found that levels of racial prejudice among white people drop significantly when they live in ethnically mixed communities, even when they do not have direct contact with minorities. Simply seeing white strangers interacting positively with ethnic minorities is enough to reduce racial prejudice.

The researchers have called this positive effect 'passive tolerance', likening it to the negative effect of 'passive smoking' where a smoky environment can increase your risk of lung cancer, even if you do not smoke yourself.

Using survey data from seven studies conducted between 2002 and 2011 across England, Europe, the USA and South Africa, the team investigated people's attitudes towards different ethnic groups. The results, published this week in Proceedings of the National Academy of Sciences, show that even prejudiced people who avoid contact with other groups become less prejudiced when they live in areas where different ethnicities mix.

'We have shown that positive contact between people belonging to different ethnic groups leads to more tolerant societies overall,' said Professor Miles Hewstone of Oxford University's Department of Experimental Psychology, senior author of the study and Director of the Oxford Centre for the Study of Intergroup Conflict. 'Astonishingly, we don't just see reduced prejudice among people who have direct contact with ethnic minorities. It isn't even confined to those whose friends have contact with minorities. Simply living in a neighbourhood where other people are mixing with minorities is enough to reduce racial prejudice.'

To rule out the possibility that more tolerant people simply choose to live in more diverse areas, two of the seven studies were conducted over several years to see how attitudes changed over time. They showed that even the most prejudiced people who did not mix at all with ethnic minorities became more tolerant over time when they lived in areas where others were mixing.

'If two white people with identical views went to live in different postcodes for a year, the person in the neighbourhood with more mixing between ethnic groups would likely leave more tolerant,' said Professor Hewstone, 'We would see this effect even if they never personally spoke to people from other ethnicities. The size of this "passive tolerance" effect on people's prejudice is of the same order as the effect of passive smoking on lung cancer risk.'

As part of the wider analysis, the team surveyed 1,056 German nationals from 50 districts in Germany, each with a different proportion of ethnic minority residents. These respondents all completed surveys in both spring 2010 and 2011 to monitor changes in attitude and behaviour. This work was led by Dr Oliver Christ of Philipps-University Marburg and the University of Hagen, lead author of the study.

German nationals taking part in the survey were asked how many of their friends were foreigners, how often they spoke to foreigners and how often foreigners helped them out. Prejudice was assessed by asking participants how much they agreed with statements suggesting that there are too many foreigners in Germany, that foreigners burden the social security system and that foreigners should be deported if jobs become scarce.

'Our results clearly show that districts with the most mixing between ethnic groups lead to the highest reductions in racial prejudice,' said Professor Hewstone. 'Although our recent longitudinal studies were conducted in Germany, there is no reason to believe that these effects would not be the same across the world. The cross-sectional studies conducted in England, the USA, and South Africa certainly support this idea.

'Governments should do more to encourage different groups to mix with each other, as we now know that this reduces prejudice not just in individuals but throughout entire neighbourhoods. Social interventions that aim to increase contact between groups will help to establish more tolerant social norms in society. In the long run, this should lead to more harmonious neighbourhoods.'