THREAD Cambridge Crime Harm Index (CCHI) & use for targeting. Had a quick look at some TVP data as this was bugging me. In 1 year 1 police area had 418 individuals making up 95% of CCHI total for that year, let’s call them the power-few (note 3.3Kindividual suspects that year)1/7 https://twitter.com/lewis_mayling/status/1337481288874340356

In fact nearly 70% of CCHI for the year is contained in 136 individuals so it is certainly possible to identify a relatively small group of high harm individuals, however how may of them continue to be high harm over time is critical to being able to focus resources 2/7

So I’ve checked this survival into the next year. The CCHI for the 418 individuals is an annual accumulative CCHI equivalent to a robbery (365 days) so a good proportion may well be in prison the next year. If we take the same threshold for the following year ie 365+ 3/7

We have 632 individuals who meet that test. Of those only 22 were in the power-few group the previous year. Of the 418, 102 were charged with at least one count of robbery or more serious. Of this 102 only 3 appear in the next years power-few 4/7

Clearly they may not all have been convicted or if they were the sentence may not have been a custodial. So how about those who are not charged who are suspected of a robbery or more serious? There are 196 that fit into that category and 11 appear in the next year 5/7

That is a very small number and a number that could be suitable for focused diversion/deterrence but identifying a potential future power-few based on previous power-few status is challenging 6/7

It seems many may be convicted likely in custody & this is partly a challenge of the “steps” in CCHI, but it does still offer significant value over crime counts & a opportunity to identify high-harm individuals, but need to understand only a few remain high-CCHI over time 7/7