Iraq stopped using leaded petrol in 2011. The lead/crime hypothesis postulates a 22 year time-lag. So if Iraq becomes a lot more peaceful in 2033 you'll know wh

Iraq stopped using leaded petrol in 2011. The lead/crime hypothesis postulates a 22 year time-lag. So if Iraq becomes a lot more peaceful in 2033 you'll know what's up. Incidentally, the list of countries where leaded petrol is still used, or was banned most recently, is basically a list of countries where bad things happen: "Algeria, Iraq, Yemen, Myanmar, North Korea, and Afghanistan". But the causality probably goes the other way; leaded petrol is cheaper.