Murders up or murders down? The strange world of homicide statistics

Did the number of murders in London increase or or decrease last year? It depends whether you mean calendar year or financial year.

Most headlines last week focused on the increase in UK murders to their highest level in a decade (or alternatively, lower than they were in 2007). Other reports went on the record level of knife crime offences (since comparable records began in 2011).

This fits in with the general picture in London, which saw an increase in the number of homicides (both murder and manslaughter) to around 130*, the most since 2008. The Metropolitan Police recorded the most knife offences (14,660, a one per cent rise since 2017).

But then another perspective was offered by the Metropolitan Police themselves, who released their latest financial year statistics (April 2018 to April 2019), which showed a significant drop in homicides from 163 in 2017/18 (or 154 not including terror attacks) to 122 in 2018/2019. The force was also able to highlight a reduction in knife injuries by 9.6% from 4,732 to 4,277, although there was a 0.5% increase in total knife crime offences (which would include possession offences).

The police say this is evidence that they have made progress in “tackling and reducing violent crime in the capital”. Perhaps it is also evidence that putting more effort and resources into policing, as a result of the outcry at the sharp spike in murders in early 2018, can affect the crime rate. We can only hope it points towards a significant reduction in murders in 2019.

Then again, it may simply be a reflection of the variation in the number of murders every day, week and month. The sharp rise in murders in February and March 2018 (19 and 20 respectively**) were enough to prompt headlines stating that the London murder rate had overtake New York’s (but you only looked at those two months, ignoring January 2018 or the year as a whole etc). The figures for the rest of the year, and the start of 2019, were significantly lower, although there were 15 homicides in March this year.

This variation in the number of murders over short periods is one reason why most murder statistics are analysed by year rather than by day, week or month. For example, in July 2008 there were four murders in London in one day. You could have viewed this as a sign of increasing violence in society, or you could have concluded that having four murders in one day was highly likely to happen once every three years.

Conclusion: Statistics are useful, as long as you know what you are looking at and can see how they vary over different time periods.

*we counted 129, the Metropolitan Police say 136, and media reports give figures varying between 132 and 135. It depends which cases you count as homicides.

**our figures, the Met say 18 for both months, but they can record cases differently depending on when they declare a case a homicide (rather than when the victim died).

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