When I tried to find data on this what I found was a mess. The violent crime rates are easy to compare, its the rates of violence by police in different countries thats a pain. Even just the US, the pre-Ferguson FBI/BJS figures are much lower than Guardian or Washpo's tracking
Im suspicious of the BJS/FBI numbers, but I'm also suspicious of the Guadian and Washpo. If we take Britain, or Norway, or France, do we know that their reported police violence figures are any better than the pre-Ferguson BJS/FBI? As a layman its hard to know what to trust