Kirk A. Johnson served 13 months as the chief statistician for Ambassador Crocker and concludes that the numbers for violence are probably gross underestimates:
Sectarian casualties are only a fraction of total civilian casualties, and such numbers lack meaning in ethnically or religiously homogeneous communities.
In particular, sectarian violence measures miss between 35 percent and 65 percent of civilian casualties on a month-to-month basis.
Violence statistics collected by the military should be viewed as a lower-bound estimate because they tend to miss smaller incidents.
McClatchy gives us some sense of what the real numbers may be:
Overall, civilian casualties in Iraq appear to have remained steady throughout the siege, though numbers are difficult to come by.
According to the Iraqi Ministry of Interior, 984 people were killed across Iraq in February, and 1,011 died in violence in August. No July numbers were released because the ministry said the numbers weren't clear.
But an official in the ministry who spoke anonymously because he wasn't authorized to release numbers said those numbers were heavily manipulated.
The official said 1,980 Iraqis had been killed in July and that violent deaths soared in August, to 2,890.