Impact of cannabis depenalization on crime in Lambeth

¶ … Crime and the Depenalization of Cannabis Possession: Evidence from a Policing Experiment" -- published in the Journal of Political Economy, a bimonthly peer-reviewed journal issued by the University of Chicago -- is a fascinating quantitative analysis on the impact of a localized policing "experiment" conducted over the course of seven and a half years. Between April 1998 and January 2006, the south London borough of Lambeth instituted a policy of "depenalization" for cannabis possession and consumption, the LCWS or Lambeth Cannabis Warning Scheme (Adda McConnell Rasul 2014, 1133). Although marijuana still remained illegal, the police in Lambeth made it known that "(i) the possession of small quantities of cannabis for personal consumption was still a recordable offence, but would no longer lead to the individual being arrested; (ii) the primary motivation was to free up police time and other resources to focus on crimes related to other drugs or other non-drug related crimes; (iii) the policy did not alter penalties for cannabis supply" (1135). Adda McConnell and Rasul undertook to examine the overall statistics related to crime that were recorded by the Lambeth police over the course of this seven and a half year period, to determine if this "policing experiment" had any noteworthy effect on crime.

Methods

Adda McConnell and Rasul wanted to examine the police statistics from two different angles. For a start, they wished to find out if the policy that had been stated publicly by Lambeth's police was actually effective. The police had made it clear that they intended to focus their efforts on policing drug crimes related to other more addictive or dangerous drugs instead of cannabis, and on policing non-drug-related crimes. For the first portion of this, Adda McConnell and Rasul were required to assemble all relevant quantitative data to enable them to make an analysis, as to whether Lambeth police had better results by focusing their policing on other drugs. They describe their data collection, measures and instruments, and techniques thus:

We use administrative records obtained from the London Metropolitan Police Service (MPS) to construct a panel data set on crime for all 32 London boroughs for each month from April 1998 until January 2006. This contains information on the number of recorded offences at two fine levels of detail: (i) the number of criminal offences related to any given drug type, e.g. cannabis, heroin, cocaine, etc.; (ii) for each drug type, the specific offence committed: possession, trafficking, intent to supply etc. Such detailed measurement of drug crime allows us to assess the impact of the policy (1136).

Using the full administrative records for the MPS across London as a whole, Adda McConnell and Rasul additionally compile statistics for seven non-drug-related crimes: assault, sexual offences, robbery, burglary, theft, fraud, criminal damage (1137). The goal is to compare police results in Lambeth during the experiment with those in the other 31 London police precincts on all of these variables.

Discussion

One of the difficulties of a study like this is that the scholars have no control over the "experiment": this experiment was a police strategy that was intended primarily as a way of allocating resources effectively. Lambeth's police chief was not thinking about social science. As a result, the comparative data sets are drawn up by Adda McConnell and Rasul as best as possible -- and obviously comparing Lambeth versus the other 31 police boroughs in London offers a valid glimpse of the actual effects of the change in police strategy. However, one is left wondering about variables that the authors do not discuss. Lambeth made public announcement of its depenalization experiment, and had the instant result of a 29.3% increase in recorded cannabis crimes (with no arrests). This essentially sounds like city-wide "drug tourism." Scientifically it would be nice to compare Lambeth's open policy with a situation where depenalization was instituted without making a public announcement. However the overall point of the paper -- that police resources are better used on crimes more serious than cannabis -- seems valid.