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Criminologist refutes cannabis-related crime increase claims

Criminologist Professor Alex Stevens has refuted media reports that reducing penalties for cannabis possession has led to increased drug use, crime and health problems. He said published data shows that these claims are unfounded and in fact highlight that cannabis use and crime have gone down since the 2004 declassification of cannabis to a class C substance.

He said: ‘Government policy on cannabis hit the headlines again recently, when both the Daily Mail and the Daily Telegraph ran articles on it claiming reductions in penalties for users of the drug have increased both crime and drug-related hospital admissions. If cannabis declassification did cause these effects, it would be an interesting and novel finding. Most researchers who have studied this issue have found little evidence of changes in use or related harms as a result of changes to penalties for users.

‘There are two national surveys that provide information about trends in cannabis use. The British Crime Survey (BCS) includes people aged 16 to 59. The Survey of Smoking, Drinking and Drug Use among Young People in England includes school pupils aged 11 to 15. Eleven per cent of 16 to 59 year-olds reported that they had used cannabis in the year before cannabis was moved down to class C in 2004. This figure was 13 per cent among 11 to 15 year-olds. By 2009, this figure had fallen to eight per cent in the older age group, and to nine per cent in the younger. It is very hard to square these reductions with a claim that the changes in 2004 caused cannabis use to rise. Over the same period, crime (as estimated by the BCS) fell by 17 per cent.

‘So what is the source of the claims that appeared in the Mail and the Telegraph? They are based on two papers presented to the Royal Economic Society, which remain unpublished. One of them uses rates of admission to hospital that were recorded as having been related to ‘harder’, Class A drugs. It links these rates to the period in 2001 to 2002 when the cannabis warning scheme was introduced in Lambeth, but nowhere else. It is reported to show that this caused a durable increase in hospital admissions amongst men of between 40 to 100 per cent.

‘This is quite a claim. To make us confident that it is accurate, the researchers would need to do several things. They would need to show that cannabis use actually rose, which they appear not to have done. They would then need to establish a causal link from cannabis use to hospital admissions for harder drugs. This would be possible if there were clear evidence of a ‘gateway effect’ that makes cannabis users move on to more dangerous substances. The problem is that, despite decades of searching, such clear evidence is still missing.

‘The researchers would additionally have to compare trends in Lambeth to those in other, similar places where the cannabis warning scheme was not in place. It would be very important to show that these places were not just any old borough, from leafy Richmond to suburban Havering. They would have to be inner city boroughs, with similar socio-economic problems and drug markets to Lambeth. And finally, the researchers would have to assume that nothing else was going on in the period after 2001 that would affect the data. They would have to ignore, for instance, the rise of the crack market in this decade. This caused havoc in the lives of many Lambeth drug users. The press reporting of this research gives no indication that these problems have been solved, and so we should have very little confidence in this reporting.

‘We are even more justified in disbelieving the claim of increased crime, given that the authors of this research have already distanced themselves from it. The research, by Nils Braakmann and Simon Jones, uses a national survey of self-reported offending in the years before and after the 2004 reclassification. The Mail claims that it shows increases in cannabis use and other crimes after penalties for cannabis were relaxed. In his response to the press reports, Dr Braakmann stated that his research ‘does not demonstrate an absolute increase in real-terms in cannabis consumption since declassification’. Rather, he said that it shows an increase amongst people who previously did not consume cannabis. Of course, cannabis use amongst people who had never used cannabis could only go one way: up. To prove that this increase was affected by the 2004 changes would be very difficult to do, and has so far not been done. If we do not know that declassification increased cannabis use, we can be no more confident that it increased crime.

‘So we are left with the best data we have on cannabis use and crime, from the two national surveys of adults and school children. They show that both cannabis use and crime - far from increasing after the 2004 declassification - actually went down.’

Alex Stevens is Professor of Criminal Justice within the University’s School of Social Policy, Sociology and Social Research.



Contact: M.J.Herrema@kent.ac.uk

Story published at 12:52pm 8 April 2013

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Last Updated: 12/06/2013