War Death Estimates that are Lighter than Air

I’m in the middle of reexamining the data collected by the University Collaborative Iraq Mortality Study (UCIMS) (This is joint work with my former student Stijn Van Weezel.)

The number of excess deaths estimated by the UCIMS is 405,000, 461,000, 500,000, more than 500,000…. well, that’s the point….it’s not clear exactly what the UCIMS estimate is but it has a natural tendency to rise.14345365-Hot-air-balloon-flying-up-to-the-sky-rising-high-as-a-symbol-of-adventure-and-freedom-on-a-blue-summ-Stock-Photo

The abstract of the paper states:

From March 1, 2003, to June 30, 2011, the crude death rate in Iraq was 4.55 per 1,000 person-years (95% uncertainty interval 3.74–5.27), more than 0.5 times higher than the death rate during the 26-mo period preceding the war, resulting in approximately 405,000 (95% uncertainty interval 48,000–751,000) excess deaths attributable to the conflict.

OK, this seems crystal clear; the central estimate is 405,000.  (It’s rather absurd to carry the numbers out to the nearest thousand despite an uncertainty interval 700,000 deaths wide but at least we know that the estimate centres around 400,000.)  The estimate of 405,000 is confirmed three times in the paper, not that confirmation should be necessary since the abstract must surely contain the right number.

But wait, there’s more:

Our household survey produced death rates that, when multiplied by the population count for each year, produced an estimate of 405,000 total deaths. Our migration adjustment would add an additional 55,805 deaths to that total. Our total excess death estimate for the wartime period, then, is 461,000, just under half a million people.

To support their upward adjustment the UCIMS authors say that there are 2 million refugees outside the country, that these divide into 374,532 (not 374,531?) households and that 14.9% of Iraqi refugee households suffered at least one death.  The 14.9% figure comes from a reference that seems to be unavailable but let’s just accept it.    These numbers would, indeed, imply around 56,000 deaths but not 56,000 excess deaths.

Readers of this blog will recall that excess deaths are deaths above and beyond some baseline level.  The excess-deaths concept is meant to capture deaths that would not have happened if war had been avoided.  The UCIMS estimated the baseline to be 2.89 per 1,000 per year (maybe 2.89857 would have been a better estimate?).  This is an extremely low baseline and, of course, if we raise it then then the excess death estimate of 405,000 will fall but leave this point aside.

Here I just note that even if all 56,000 estimated deaths from the refugee households occurred in a single year the death rate for these households would be around 2.8 per 1,000 for that year, slightly below the baseline used by the UCIMS.  So even if we lard on far more deaths than the 14.9% figure suggests it would still be quite a challenge to squeeze a positive number of excess deaths out of this situation.  It seems that refugees have, on average, done better than the people left behind in Iraq.  So integrating refugees into an excess-death calculation should lower the estimate, not raise it as claimed by the UCIMS authors.


Still, no one associated with the article seems prepared to stop even at 461,000.  Indeed, the very next sentence after the one quoted above switches from “just under half a million people” to “about half a million excess deaths”:

Our total excess death estimate for the wartime period, then, is 461,000, just under half a million people.


We estimate about half a million excess deaths occurred in Iraq following the US-led invasion and occupation (March 2003–2011).

Surely the PLoS editors will take the punch bowl away from the inflation party:

….their final estimate is that approximately half a million people died in Iraq as a result of the war and subsequent occupation from March 2003 to June 2011.

I guess not.

The next step is for lead author Amy Hagopian to use the media to pretty much convert the half a million number into a lower bound:

“We think it is roughly around half a million people dead. And that is likely a low estimate,” says Hagopian.

Finally, something important has been lost in the shuffle as we have traced the trajectory of the ICIMS estimate from 405,000 up to 500,000+.

The uncertainty  interval has disappeared.  

We started out with an uncertainty interval of 48,000 to 751,000 and we ended up with 500,000 as “likely a low estimate.”  Somehow, the back-of-the-envelope calculation on Iraqi refugees airbrushed all downside uncertainty off the books.  The last remaining question seems to be: by how much should we pad the half-a-million figure?



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