Statistics might explain why people sometimes blindly cross the road as soon as they see others doing so, without first checking it's safe, researchers say.

Biologist Dr Ashley Ward of Australia's University of Sydney and colleagues are looking at the statistics behind collective decision-making.

They are seeing if the rules that govern how fish make decisions apply to humans.

Their fish study, published online today in the Proceedings of the National Academy of Sciences, shows that fish are led into danger when just two fish swim towards a predator.

This is the first such 'quorum response' study in vertebrates, says Ward.

Ward's team tested what happens when real fish swim with a robot fish that the researchers could make move towards a predator.

The researchers found that the real fish almost ignored one robot fish.

But when there were two robot fish, the real fish followed them towards the predator.