Why you can't identify changes in crime by comparing this month to last month

This post first appeared on the Social Research Association blog. Understanding if some event is associated with a change in the frequency of crime is a common question, both in practice and in research.

Chart: 73% of victim-based crime is not reported to police

Of the 10.9 million crimes which individual adults aged 16 years and over experienced in the past year, only 27% were reported to the authorities. Reporting rates vary substantially, with more-serious crimes more likely to be reported.

Chart: Homicides haven't only increased in Britain

The homicide-rate increase over the past five years hasn’t been unique to England and Wales, with murders also increasing in France, Germany and Sweden after continent-wide decreases since the 1990s.

Chart: Seizures of the most harmful drugs at UK borders are falling

Border Force is responsible for seizing drugs at ports, airports and international parcels depots. However, reports by the Chief Inspector of Borders and Immigration suggest drug-detection efforts are hindered by understaffing, lack of training and focus on conducting passport checks on travellers.

Chart: In five years, crime-related demands on police have almost doubled

One way to understand crime-related demands on police forces is to track ‘crime pressure’, a measure of investigative workload representing the number of crimes reported to a force per officer, weighted according to Office for National Statistics estimates of the relative severity of different crimes.

Chart: Much of the homicide drop has already been erased

The rapid decrease in the homicide (murder, manslaughter and infanticide) rate in England and Wales between 2000 and 2014 was unprecedented over the previous century, but a third of that decrease has already been reversed.

Chart: Online crime now the most-likely threat to many businesses

Online crime (including hacking, phishing and virus attacks) is now experienced by more businesses than any other type across sectors as varied as manufacturing and communications. But in the sectors most-likely to experience a crime (retail, accomodation and entertainment), traditional offences such as theft are still more likely.

Chart: Drug use was falling, but that seems to be changing

Self-reported drug use has fallen for most of the past 20 years according to the Crime Survey for England and Wales, but in the past seven years the use of cannabis, cocaine and ecstasy has increased substantially, particularly among people aged 16–24.

Chart: Homicide methods are changing

Homicide (murder, manslaughter and infanticide) in England and Wales is rare, with about 12 homicides per million people last year, a similar rate to a decade ago. But homicide methods are changing: the rise in knife murders is well known, but there are other changes, too.

Chart: Almost 7 million adults have been victims of partner abuse

Among the 42 million adults in England and Wales aged between 16 and 74, 1.3 million have been sexually assaulted by a current or former partner, 4.3 million subjected to non-sexual assault and 2.