But some psychologists argue that when we use violence, even as a deterrent, we model and encourage violence in observers. A classic example is capital punishment; advocates of the modelling theory suggest that, rather than deterring criminals from committing murder, capital punishment contributes to a rise in homicide rates. They argue that it's not what we teach which has most impact on our students, but how we behave; that the human propensity to copy models is one of the most powerful driving forces in our psychology.
Supporters of capital punishment argue that publicised executions are a powerful deterrent for potential killers. Opponents point out that most homicides are spontaneous events, carried out in the midst of highly charged social conflicts. Such "spur of the moment" acts are unlikely to be inhibited by "second thoughts". They say that capital punishment is irrelevant as a deterrent.
New evidence suggests that potential killers may identify with the executioner rather than the executed. They might also feel that, by promoting capital punishment, society is demonstrating the low value it puts on human life. This might explain why, in the longer term, executions are followed by a rise in homicide rates.
Ernie Thompson, assistant professor of sociology at the University of Houston, has published statistics that show homicides increase by 22 per cent in the eight months following an execution in California.
Other data supports this "brutalisation" theory. For example, after the execution of Charles Troy Coleman in Oklahoma in 1990, which followed a 25-year suspension of capital punishment in the state, homicide rates rose.
A similar rise followed the 1992 execution of Donald Eugene Harding, the first in Arizona in almost 30 years.
A more detailed analysis of Thompson's research does show an initial dip in homicide rates in the first month following an execution. But this soon rose to levels significantly above those before the execution. This temporary "death dip" has been observed before. For example, a study of homicide rates following executions in London between 1858 and 1921 found a drop in the week after, but rises over the next few weeks. Intriguingly, this dip appears to be due to a sharp fall in planned homicides; the increase in the following months to more impetuous crimes.
So it seems that executions appear to act as a deterrent for a short period, but that this effect quickly wears off. In the longer term, capital punishment brutalises society, leading to a long-term rise in homicide rates. Educationists should therefore be deeply concerned about the role models who influence our children. Are these not models, including our politicians and leaders, who regard aggression and violence as the means of solving problems? What do we think our pupils are learning from this?
Professor Raj Persaud is a consultant psychiatrist at the Maudsley hospital and senior lecturer at the Institute of Psychiatry in London. He is this year's visiting Gresham professor for public understanding of psychiatry and will give a free public lecture at Barnard's Inn Hall, London EC1 on November 24. See www.gresham.ac.uk for more details. Email: email@example.com