Tuesday, November 06, 2007

U. S. Monthly Deaths in Iraq

I wrote yesterday about changes in opinion of the Iraq war. In the process I said that the death toll is rarely presented in systematic form by news coverage. Totals, or totals for the month are frequently mentioned, but seldom in the context of the entire war. Likewise, yesterday's news story was that 2007 has now become the costliest year, with more U.S. deaths than in any previous year of the war. So let's take a little of our own medicine and put the monthly totals in context.

The last two months have indeed seen substantially fewer US losses than any previous months in 2007. April, May and June produced exceptionally high casualty counts with only 5 previous months reaching the same level of over 100 deaths. In contrast, October casualties fell to under 40 deaths, a low matched in only 7 previous months.

But looking at the last 12 months, it is really only September and October that have been well below recent casualty rates. There is some visual impression of a sharp decline since May, but that is deceptive since May was the third highest death toll of the entire war.

The bottom line: deaths have declined recently and especially in the last two months. But that decline is from very high levels compared to the rates in the entire war. Even the "lower" September rate is actually in the middle of rates for the war as a whole.

There is a lot of month-to-month variation in the death rate. That makes it a bit hard to see the systematic trend in the midst of the variability. The plot below shows the trend in deaths, abstracting out the noise of month to month variation.

We see three clear phases. After the invasion, deaths fell to about 45 per month and stayed there until early 2004. Then the rate increased over a period of about 4-6 months to a new and more intense rate of about 67 deaths per month. This became the status quo death rate for the second half of 2004, all of 2005 and the first half or so of 2006. Late 2006 saw an increase which peaked in the first half of 2007, with an apparent fall since. The current trend estimate stands at the low 60s, not much different from the 2004-2006 level. Unless the very low casualty rate of October becomes the new norm, we are back to about where we have been since mid-2004. It seems more likely that October will prove to have been unusually low and November and subsequent rates will return to around 60 deaths per month. (This is a statistical, not a military judgment. At the moment, October looks out of line with the rest of the data, so a good statistical guess is that subsequent months will be closer to the trend. Of course if conditions or tactics have changed in ways that actually reduce the risk, then casualties can remain near October's low level.)

Yesterday my point was that opinion on the war has turned somewhat more positive, but that while changes in the "objective" facts of the war might contribute some to that shift, the stronger driver of opinion was political debate from Washington. Looked at over the entire course of the war, there have been large month-to-month changes in the casualty rate. Opinion on the war shows no evidence of such high variability, as it should if opinion of the war simply and directly mirrored contemporaneous casualty rates. Rather we've seen a pretty consistent long run decline in positive views of the war, but in 2007 a flattening of the trend followed by a recent rise in positive views of the war. Those changes came despite the substantial rise in casualties in 2007. There is little evidence of a direct link of opinion to current casualty rates.