A parting on the right

The police forces of England and Wales implemented a new set of rules for recording crimes in 2002-3, following earlier piecemeal adjustments in 1998-9. The National Crime Recording Standard (NCRS) was designed to be more victim-friendly than the counting rules which had preceded it: rather than the police insisting on corroborating evidence before a crime was recorded to have happened, a crime was to be recorded whenever one was reported unless there was evidence to the contrary. There was a certain amount of resistance to these changes, which had the direct effect of apparently increasing the crime rate and the indirect effect of lowering the police’s clear-up rate. Nevertheless, the Home Office felt very strongly that police figures were far too low – the British Crime Survey, based on reports from a representative sample of individual victims of crime, suggested that only about 25% of predatory crimes were getting into the police figures – and the changes duly went through. Comparability was also an issue, although less of an issue with each passing year of data being produced under the new rules. The Home Office has in any case made it very clear that there is no comparability of police crime figures between 2002 and 2003, making available figures like the ones from which the graph below was compiled.

As you can see, there’s a strong correlation between the impact of the NCRS and the amount of evidence typically left by the offence. Recorded burglaries weren’t greatly affected, but recorded crimes of personal violence – where supporting evidence is particularly thin on the ground – went up by almost a quarter from one year to the next, on the basis of nothing other than a change in counting rules.

Now, there is no particular reason why the average member of the public should know about all this. It’s inconceivable that anyone with a professional or academic interest in crime or policing wouldn’t know about it, though; it would be like claiming expertise in English history and getting the date of the Battle of Hastings wrong. So this was an interesting story about the Shadow Home Secretary, Chris Grayling.

Sir Michael Scholar, chairman of the UK Statistics Authority, has warned [Grayling] that the way he used figures for violent crime were “likely to mislead the public”. … Mr Grayling’s office arranged for a press release to go out in every constituency in England and Wales, purporting to show that violent crime had risen sharply under Labour, as part of a campaign spearheaded by Mr Cameron about “broken Britain”. But Mr Grayling had failed to take into account a more rigorous system for recording crime figures introduced by the Home Office in 2002. … Mr Grayling has used comparison between the figures before and after the rule change to suggest that the Labour government has presided over a runaway rise in violent crime.

“I do not wish to become involved in political controversy but I must take issue with what you said about violent crime statistics, which seems to me likely to damage public trust in official statistics,” Sir Michael wrote in a letter to Mr Grayling yesterday.

Mr Grayling replied by promising to “take account of the request by the Statistics Authority, particularly with regard to the changes to recording practices made in 2002-03”. But he insisted that he would “continue to use recorded crime statistics, because they reflect an important reality; that the number of violent crimes reported to police stations, and particularly serious violent crimes, has increased substantially over the past decade, even taking into account any changes to data collection”.

But we don’t know the number of violent crimes reported to police stations, because we don’t know the number which are reported but not recorded; that number is not recorded, surprisingly enough. (There was a proposal a few years back to keep separate tabs on ‘incidents’ (i.e. everything that comes over the front desk or over the phone) and ‘calls for service’ (the subset of incidents that the police do anything about), but as far as I’m aware it didn’t come to anything.) In other words, Grayling has not only managed to ignore a really basic piece of statistical general knowledge; he’s gone on to ignore a correction by an expert in the field, responding in a way which demonstrates a complete lack of understanding of what he’d just been told.

The question this leaves is, is David Cameron’s first choice for Home Secretary very, very dishonest, or just very, very stupid?

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