Jargon buster – the ‘clear-up’ rate

How to achieve a 120% clear-up rate for burglary

The burly, rather frightening, Detective Chief Inspector boomed into the shabby Criminal Investigation Department at Brixton Police Station. “Well that’s it! We can all stop working until Christmas.” Once the dutiful cheering had subsided it was revealed that a local burglar had confessed to a huge number of burglaries, over 120% of them in fact, thus negating any further need for the detectives to do anything for the rest of the year. And, it was still only February.

The mathematically improbable 120% “clear-up” rate would lead to no promotions, no financial bonuses for the chief or anyone else, there would simply be a momentary ‘feel-good factor’ of a job well-done. The detectives would in fact not be taking the rest of the year off, the chief  was merely exercising a well-understood joke, at the expense of more senior officers and politicians who were thought to believe that clear-up rates were useful to judge police ‘performance’.

What is the clear-up rate?

The clear-up rate compares two different sets of data: the number of crimes recorded in a period of time and the number of crimes solved in the same period. It does not tell us how many of the crimes that were recorded were solved. This is because crimes generally get recorded at one point in time and get solved months, or even years, later. In our Brixton example, let’s say 100 burglaries were recorded in January and February and our burglar confessed to 120. This gives us 120% even though most of the crimes he confessed to were recorded the previous year (or even earlier).

Even Sherlock Holmes had to take some time to solve crimes.

The true story above dates from 1990, so we have been using clear-up rates in the British police force since at least then. Politicians and journalists have said that ‘clear-up’ rates are too high or too low, for just as long. Clear-up rates are never ‘about right’ or ‘reasonable’, You wonder why the police publish them at all, for all the grief they get in return.

The reason is that the ‘clear-up’ rate is quite useful for understanding comparative police performance over time or between locations. But they need to be treated with caution and seen in context (which they normally aren’t).

Clear-up rates are different depending on the type of crime

Clear-up rates vary a lot according to the type of crime. The clear-up rate for drug dealing is normally close to 100%, because police only record the arrest of drug dealers not all the individual deals. The clear-up rate for street robbery is nearer 5% or less, because it is an especially difficult crime to solve. An amalgamated clear-up rate for different types of crime is likely to be nonsense, combining things that are too different to be fairly compared.

Strength of the clear-up rate

Despite the weaknesses, the clear-up rate is the best way anyone has found to measure police detection. We are stuck with the clear-up rate until someone solves the conundrum of how to do it better. Conundrums are much harder to solve than crimes, so don’t hold your breath.

Let’s try and make the best of it, by understanding how it works.

Weakness of the clear-up rate

Clear-up rates make more sense the bigger the area and the longer the time they cover. This because they are volatile, as demonstrated by our Brixton burglar. His performance had a huge impact on the clear-up rate for January and February in Brixton. It would barely cause a ripple over the year for the whole of London.

Why do we bother having a clear-up rate?

You might wonder why the police bother with solving old crimes. Shouldn't we just focus on the here and now? Well crime matters to victims. At a practical level, stolen property might be recovered and returned. More importantly people want to know if the person who invaded their home was caught, they still want to know years later, I would say they have a right to know. The burglary took place on one day, the hurt and fear carries on, sometimes for years, it may be eased by the closure of knowing the person was caught.

Solving old crime helps solve future crimes. Understanding how crimes are committed by talking to the person who did the crime, may reveal techniques, choices of property taken, other offenders, vulnerabilities of premises or products. There’s a gold mine of crime prevention intelligence to be had. Some burglars, for example, choose to commit crimes near where they plan to sell the stolen property. This information would be extremely relevant to an anti-burglary campaign.

Crime recording

Crimes get committed, some of them get reported and some of them get recorded. The gap between what gets committed and what gets recorded – this ‘dark figure’ of crime can be very large. For more information check out this academic study by Mike Maguire and Susan McVie .

Finally – the war on dirty money

Clear-up rates will continue to be used. Fundamentally, they compare something we control (the amount of crimes we solve) with something else we control (the amount of crimes we record). We can be held accountable for things we control, that seems only fair.

On a positive note, I think the clear-up methodology has something to offer how we measure criminal money. Currently we compare the amount recovered with the amount that criminals have made. This creates wild statistics like 99.74% of criminals keep their proceeds of crime (the National Audit Office’s absurd figure for the UK).

We could compare something we control – the amount we have recovered with something else we control, the criminals we have caught. Then we can hold people to account. My next post will develop this idea

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