The young woman knocked off her bicycle was being loaded into the ambulance. "Is there anyone who can go with you to the hospital?" a policeman asked - but she racked her brains in vain. Her mother was in Belgium, her friends were all on holiday; she would have to go through hours of tests alone. Then a stranger who had collected her scattered belongings spoke up: "I'll go with you," she said.

This story was told recently on BBC Radio 4's Saturday Live programme. Each week, listeners are invited to phone in with their experiences of being helped by people they did not know, and to thank them. There is no shortage of moving tales about small or extraordinary acts of kindness which have made an enormous difference.

Kindness has always been regarded as an essential human trait. One of the best-known stories in the Bible is the parableA story told with a moral or spiritual purpose. of the Good Samaritan. In it, Jesus tells of a Jewish man who is attacked by bandits and left lying half-dead on the roadside.

The first person to find him, a priest, crosses to the other sideThe popular phrase "pass by on the other side" means to ignore someone in need of help. of the road and leaves him to his fate. So does the second. But the third - a Samaritan whose people are traditionally at odds with the Jews - tends to his wounds and takes him to an inn, where he pays the owner to look after him.

When, in 1953, a clergymanChad Varah set up the Samaritans after officiating at the funeral of a 14-year-old girl who had committed suicide. had the idea of setting up a telephone hotline for people in distress, his organisation came to be known as the Samaritans. Today it has over 20,000 volunteers working for it in the UK. Its offshoot Befrienders Worldwide operates in 32 countries and handles more than seven million calls a year.

Yet kindness has not received as much attention from psychologists as one might expect. One expert, Robin BannerjeeThe head of the department at Sussex University which is carrying out the survey., found just 35 papers about it in psychology journals from the 1980s. Now that is changing: in the last 10 years there have been more than 1,000.

To investigate kindness in today's world, the University of Sussex has launched an enormous public project in conjunction with the BBC. Called the Kindness Test, it invites anyone over 18 to fill in an online questionnaire about their experience of and attitudes towards kindness.

According to the organisers, some key facts have been established by previous research. One is that being kind to others makes us feel better about ourselves.

In an experiment in VancouverA city on the west coast of Canada which is consistently named as one of the best places in the world to live., people were given envelopes of money to spend. Half were told to buy things for themselves, and half to buy things for others or give the money away. At the end of the day, those who had spent it on others turned out to be significantly happier.

In another experiment, people were asked to complete a boring task on a computer which then lost all their work. Half were shown a funny film to cheer them up, while half were sent a researcher posing as an IT expert who kindly solved the problem for them. Those who had been helped proved more inclined to carrying on helping the experiment's organisers - suggesting that kindness is contagiousSpreads from one organism or person to another. .

Can kindness be catching?

Some say, yes. Most people are good-hearted, but get so distracted by the demands of everyday life that they do less for others than they could. Witnessing an act of kindness, or being on the receiving end of one, reminds them of the wonderful bond it creates between people - particularly strangers - and encourages them to go out of their way to be helpful.

Others argue that kindness depends on character rather than example. Some people are instinctively kind and rise to the occasion whenever anybody needs their help. But some are simply selfish and will not lift a finger for others: they see the fact that so many people volunteer for organisations like the Samaritans as an excuse not to get involved themselves.