How can you tell if someone's lying? The answer is, they're probably not.

Traditional economics says that people are rational beings who will lie if it's to their advantage. A recent university study has shown that, actually, we're pretty honest - especially when we're at home.

Researchers in Germany phoned people at home and asked them to toss a coin. There was a strong financial incentive to fake the result: if the coin landed tails-up, the participant would receive money or a gift voucher, while if the coin landed heads-up, they would get nothing. Because they were on the phone, they knew there was no risk of getting caught if they lied.

And yet people told the truth. Over hundreds of tosses a coin will land tails-up roughly 50% of the time. In this study over half the people asked (55.6%) said that the coin landed heads-up, which meant they would receive nothing.

Previous studies had found that people were more deceitful. In those laboratory studies 75% of people reported a winning coin and claimed a reward. So the research team thinks it's being in our own homes which makes us play fair, although it's not yet clear why.

In fact both types of study show people are surprisingly trustworthy. Even in the laboratory, 25% of people turned down a reward by telling the truth. The researchers say this is because honesty is highly valued in human society. We care about our reputation and our sense of ourselves as decent people. So lying has a psychological cost and it seems this cost outweighsthe financial benefits of lying.