What Does "Safety in Numbers" Mean?

Safety in numbers is the term for the statistical belief that individuals are safer when engaging in some activities as part of a group. At first glance, this seems a common-sense prediction. The more individuals in a group, the less likely it is for any event, good or bad, to occur to a given individual. Research, however, has shown that other factors may be involved in real-life scenarios. The phrase is used by biologists to describe activity by large groups of animals. A similar concept appears to be at work in human activity such as vehicular traffic.

The concept appears to be one reason why animals cluster in large groups such as herds, flocks, or schools. This is borne out by observation. When a group of animals is stalked by a predator, the predator classically targets the animals that are too old, small, or weak to keep up with the rest of the group. Evolutionary biologists believe this has the effect of culling undesirable genes from the group, a process they call survival of the fittest. Statistical scientists see it another way. If a predator attacks a group of 10 animals, any individual animal has a 10-percent chance of being killed. If the group numbers 100, individuals face only a 1-percent chance that the predator will take them down.

This is an effective survival mechanism, and many species have developed ways to benefit from it. It is thought that periodical cicadas, insects that famously emerge in great numbers every 13 or 17 years, coordinate this behavior to benefit from safety in numbers. Predators will be able to consume only a small percentage of the overall group; the rest of the cicadas will be able to eat, fly, and breed in peace. Biologists refer to this survival technique as predator satiation. Numerous species of plants and animals practice some form of this technique.

There is evidence that safety in numbers applies to traffic safety, especially where bicycles and pedestrians are concerned. Numerous studies have demonstrated that fewer motor vehicle collisions with cyclists occur at areas or times when cyclists are present in great numbers. The common explanation is that motorists who see a large group of cyclists or pedestrians will reduce speed and watch the road more closely, while in general drivers are concerned with other vehicles and do not look for smaller, slower-moving road traffic. This stands in contrast to the purely statistical advantage of safety in numbers applied by plant and animal species.

Cycling activist groups, aware of this factor, encourage cyclists to travel in large groups when possible. Their intent is not simply to play on safety in numbers, but to increase overall awareness of the presence of cyclists at any time. Motorists who learn to drive carefully near large groups of cyclists are more likely, the theory goes, to drive carefully around individual bike riders. To this end, group cycling events called Critical Mass occur on a monthly basis in cities around the world, intended to raise awareness of cyclists in general.