Bing West suggests in the current Foreign Affairs ("Groundhog Wars", September/October 2011) that Western military casualties to Afghan civilian casualties are in the ratio 1:2. This seems a surprising statistic and given FA don't footnote, I wonder how it was arrived at.
As it's Foreign Affairs, the statistics used would have been from a "reliable" source such as NATO or the UN, and indeed the UN recently released this suggesting that whilst civilian casualties were on the rise, the culprits were the insurgents. Air strikes were named as the leading cause of civilian deaths by Western forces, here euphemistically named "Pro-government forces".
Wikipedia has an excellent table on this here suggesting that the total number of Afghans killed as a direct result of US-led action is between 6250 and 9000 people.
From iCasualties, total Western troop force deaths in Afghanistan since the commencement of Operation Enduring Freedom are cited as 2738.
Taking the lower boundary of civilian deaths fo 6250 against 2738 suggests a ratio of 1:2.3 which in the world of social science is pretty much exactly what Bing West calculated. The upper threshold suggests a ratio of 1:3.3.
Of course statistics can be argued over even when it's body counts especially when the nature of the insurgent and the civilian is relative. NATO has been constantly on the backfoot over civilian deaths and the neoTaliban have been adept at making the most of propaganda opportunities associated with this anti-humanitarianism.
Cost of war