In their concept, the idea of opportunity denotes something that is possible to do. By describing ways in which opportunities to commit crime without capture are distributed in time, place and social networks their work influenced ideas of how to block those opportunities. Better locks on bicycles, for example, could block the opportunity to steal them easily, which could in turn reduce bicycle theft. They have been instrumental in reshaping crime prevention strategies on a global scale to focus on factors that characterise situations where crimes are often committed.

Clarke and Mayhew have shown that crime prevention measures can often be quite simple, and yet highly effective. People commit or refrain from committing crime based on more than social and psychological factors; the physical design of the environment is another contributing factor. The character of buildings and the street environment, or the accessibility of valuable objects, can influence the likelihood of a crime being committed.

Prime example: Less lethal oven gas reduced suicides

Between 1963 and 1975, there was an unexpected decline in the number of suicides in England and Wales. Clarke and Mayhew then reviewed the evidence to look for any change in the opportunity structure to prevent suicide. In 1988 they published a report showing that the decline was clearly due, at least in part, to a reduction of lethality in the chemical composition of household gas. It simply became more difficult to commit suicide by just turning on the gas and lying down – then waking up alive with a headache. They concluded that the practical feasibility of carrying out a particular act has a major impact on whether or not the act will be committed – and at what rate of occurrence.

Strategies for the entire world

Clarke and Mayhew’s work has been instrumental in reshaping crime prevention strategies worldwide. Rather than focusing on the social and psychological factors that motivate offenders to commit crimes, they showed that in some cases it can be more effective to block the opportunities for carrying out what they are motivated to do. This could apply to a change in the characteristics of any of the situations where crimes are repeatedly committed.

Their work has made major contributions to the rapid development and application of ‘situational crime prevention’ in both the public and private sectors. In many parts of the world, not least in Sweden, this has led to significant reductions in the number of burglaries, auto thefts, and robberies.