In debates over criminal justice policy, people are constantly referring to crime indexes for the question of whether crime is up or down and by how much. But there are problems with the official indexes. One of them is that indexes tend to be dominated by the least serious crime chosen for inclusion in the particular index. Crimes are simply counted, and because the frequency of crimes tends to be inversely related to their severity, the less serious crimes dominate.
For example, the FBI’s index of violent crime includes murder (and voluntary manslaughter), rape, robbery, and aggravated assault. Murder is the most serious, followed by rape, but the other two are much more common. As a result, the violent crime index is largely a measure of robbery and aggravated assault, and it relatively insensitive to changes in the rates of murder and rape.
One alternative is an index with crimes weighted according to their severity. I have seen such indexes in other countries and for some jurisdictions within the United States, but none for the United States as a whole. Here is a first cut at a severity-weighted index of violent crime in the United States. Continue reading . . .