There are three problems I can see with this comparison:

1) Statistical analyses require accurate records, which aren’t available in this case. There are no records available that detail how large the opposition is, or who the members are. In fact, it’s impossible to obtain such data, as the opposition forces don’t keep such records; and in any case the records, if they were to exist, wouldn’t necessarily tell us anything since alliances are still shifting.

2) The Iraqi forces aren’t US forces. They’re not trained our forces’ levels, and they certainly aren’t equipped like our forces. Adding them into the equation is obviously going to skew the results.

3) The goal of US and Iraqi forces is to end the insurgency, not necessarily to kill insurgents. You’d need to include the terrorists that have been imprisoned to the equation.

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“Nations have no permanent friends or allies, they only have permanent interests.” - Lord Palmerston