Initial media reactions to the Norway terrorist attack

Reading the initial media responses to the awful events in Norway last week I struck by the way that (a) it was initially assumed (based on practically zero evidence) to be Al Qaeda; and (b) even after it was found to be the work of a (probably lone) right-wing Christian zealot mentions of 'a need for debate around multiculturalism and immigration' and 'jihad' kept finding their way into the reports.

I was going to write a bit more on this, but as usual others have covered it already, and better than I could.

More on police numbers and crime

More as promised on police numbers and crime. This is all based on a pretty rough and ready literature review of research since 1996, although I think I got most of the relevant papers - 13 in all. These were a mixture of observational studies using time series data, quasi-experiments and natural experiments. Below, I've copied and mildly edited the discussion section of a document I've written around this literature review. I'll add a link to the final report once it's ready.

To summarise, I'd argue that on the basis of current research (a) there is a relatively robust negative association between numbers of police officers and property crimes, broadly defined; (b) evidence of an association between police numbers and violent crime is weaker and sometimes contradictory; and (c) the 'elasticity' of property crime in relation to police numbers might be relatively conservatively estimated at approximately -0.3; that is, a 10 per cent increase in officers will lead to a reduction in crime of around 3 per cent (and vice versa).

All that said, taken individually none of the studies I looked at came close to ‘proving’ that higher numbers of police leads to less crime. Despite improvements compared with earlier work almost all suffer from potentially significant methodological and conceptual flaws. For example, some of the observational studies that use lagged effects to estimate the effect of police numbers or arrests on crime rate appear to vary the length of the lag used purely to maximise the significance of the association, without giving much if any thought as to why the time spans involved should vary by crime type.

Many of the natural or quasi-experiments rely on what are highly unusual and probably unsustainable deployment patterns that resulted from ‘shocks’, such as terrorist attacks, which are thankfully highly unusual. Furthermore, such events may initiate a context for policing far removed from the ‘day-to-day’, and the policing response to such emergencies may acquire a specific and unique symbolic meaning.  Some of these papers make some pretty sweeping claims about the potential effect of police numbers on crime that may be undermined by the specific context of the events they describe. Despite the fact that natural or quasi-experiments usually allow firmer causal conclusions to be drawn than observational studies, in this instance better evidence for a ‘general’ link between police numbers and crime rates is probably provided from the latter. 

Yet, the observational studies are likely to suffer from all the usual problems around the recording of crime and officer’s activities. For example, most are forced to use the recorded rate of crime as a proxy for the real rate. This may or may not be a valid approach, but in the absence of firm evidence either way some care is need when making claims that more police lead to less crime. Most of the studies that are not natural or quasi-experiments take no account of what police officers actually do, and how this might vary from place to place and over time, while, as noted, the experimental studies rely on highly unusual events and police deployment patterns.

Many of the observational studies also suffer from two further problems. The first is a possibly excessive faith in instrumental variables (IVs) – in many of the studies listed the robustness of the IV used is far from proven, meaning that issues of endogeneity may not have been as fully dealt with as the authors claim. That is, while the authors believe they have solved any problems created by the possibility that the crime rate affects the number of police as much as vice versa, this may not actually be the case.

The second problem is that much of the research I looked at relied on a rather simplistic ‘rational choice’ model of criminal behaviour. Thee idea here is that the commission of crime is vitally influenced by considerations of the risk of sanction weighed against potential reward, with the number of police representing one element of the risk calculation. If this is not a valid theory of crime causation, or at least one that tells only part of the story might lack a plausible causal mechanism to explain the associations between police numbers of crime many of the studies do appear to uncover. Causal claims – that higher police leads to less crime – made on the back of observational data are significantly weakened by the absence of such a mechanism.

However taken together research that has appeared over the last 15 years does indeed suggest that there is a significant negative association between the numbers of police (and/or the number of arrests made) and the level of at least some forms of recorded crime. Two things in particular support this conclusion. First there is the striking extent of agreement between most of the studies I looked at. They varied considerably in terms of methodologies, time-spans, and countries, but still generated broadly similar findings. This kind of triangulation adds some weight to the idea that there is a real effect of police numbers on some types of crime.

Second, there is the fact that the purported effect of police numbers on crime is more consistently found in relation to property crime than violent crime. This adds considerable ‘face validity’ to the overall findings. At least a proportion of overall property crime presumably is committed by individuals who weigh up the relative risks and rewards involved, and who may even pay conscious attention to the presence or potential presence of police. Much violent crime, however, is conducted in the heat of the moment in pubs or on the street, or behind closed doors in the home. In neither case would one expect consideration or even awareness of potential police attention to come into play. A uniform association between police numbers on crime might in these terms be suspicious – one would expect the potential effect of the number of officers on the rate of crime to vary by crime type. 

Of course, considerably more work would needs to be done on this topic before any firm conclusions are reached. But the current state of research is extremely suggestive, to say the least.