The crime severity index basically measures the volume of crime and the relative seriousness of crime, let's say homicide compared to petty theft, like bicycle theft. In fact, criminologists have made the case, and others who study crime outside of the academic realm have made the case, that this a measure that should be taken perhaps even more seriously than the crime rate, which measures all crime, whether it's, to use that example again, bicycle theft versus homicide.
On June 12th, 2018. See this statement in context.