The security hypothesis
Looking into crime research, a theory that apparently explains the crime drop is the security hypothesis. This theory states that:
change in the quantity and quality of security was a key driver of the crime drop.
It posits that crime has become harder because of better security measures (more locks for instance) and that in consequence people do less crime.
It matches a few observations:
The drop in vehicle theft:The impact of locks on house burglary in the UK:From evidence relating to vehicle theft in two countries it is concluded that electronic immobilisers and central locking were particularly effective.
The impact of helmet laws on motorbike theftsThe causal role of improved security is strongly indicated by a set of interlocking data signatures: rapid increases in the prevalence of security, particularly in the availability of combinations of the most effective devices (door and window locks plus security lighting); a steep decline in the proportion of households without security accompanied by disproportionate rises in their burglary risk; and the decline being solely in forced rather than unforced entries to households. The study concludes that there is strong evidence that security caused the decline in burglary in England and Wales in the 1990s.
The impact of backalley gates on house burglary in Great Britain:In London, motorcycle thefts fell by 24% on the introduction of helmet laws on 1 June 1973, from 5,280 in the twelve month period prior to the legislation to 3,997 in the subsequent twelve months (Mayhew et al. 1976). In Holland, a drop in motorcycle thefts following the introduction of helmet laws in February 1975 was noted in national victimisation survey results: the percentage of people who had experienced a theft fell from 10.0% in 1974 to 6.4% in 1975, with even lower levels in subsequent years (van Straelen 1978). These declines were presumably the result of opportunistic thefts being made more difficult by the need for the thief to have a crash helmet in his possession; otherwise, he would quickly be noticed and be suspected of stealing the motorbike.
the introduction of penalties for riding a motorcycle without protective headgear had the same unintended result in the Federal Republic of Germany
A new situational crime prevention measure recently introduced into Great Britain involves the fitting of gates to alleyways running along the back of terraced properties to restrict access to local residents and reduce opportunities for offenders. (...) in the City of Liverpool. The results demonstrate that, relative to a suitable comparison area, burglary was reduced by approximately 37%
How does it compare to other explanations for the crime drop ?
The authors of the security hypothesis say that a crime drop theory should pass 5 tests:
-
Are there reasonable empirical grounds to consider the theory ?
-
Can the theory be applied to different countries (i.e. explain why the crime decreased in all developed countries) ?
-
Is the theory compatible with the fact that crime was previously generally increasing for several decades?
-
Is the theory compatible with the fact that some crimes such as phone theft and e-crimes were increasing while many crime types were decreasing?
-
Is the theory compatible with variation in the timing and trajectory of crime falls both between countries and between crime types (some crime types decreased earlier than others) ?
Out of 15 common theories, the security hypothesis was the only one to pass all 5.