David Kane writes,

You posted before on the Burnham et al (2006) study on Iraqi mortality. I [Kane] have an R package with some preliminary analysis and comments.

My question concerns the confidence intervals reported in the prior study, Roberts et al (2004), by many of the same authors.

My question concerns the confidence intervals reported in the prior study, Roberts et al (2004), by many of the same authors. Their central result is:

“The risk of death was estimated to be 2.5-fold (95% CI 1.6 – 4.2) higher after the invasion when compared with the pre-invasion periods.”

Since they estimate a pre-war mortality rate of 5.0 per thousand, we can translate the confidence intervals given in relative risk above into a post-war mortality rate of 8.0 – 22.5. (Just multiply pre-war mortality by the new risk. I realize that this ignores the uncertainty in the pre-war estimate, but let’s ignore that complication for now.) The problem is that this contradicts the direct estimate of post-war mortality which the authors provide.

“The crude mortality rate during the period of invasion and occupation was 12.3 per 1,000 people per year for the post-invasion period. (95% CI 1.4 – 23.2)”

In other words, their direct measure of the confidence interval for post-war mortality is so high that there is no way that their confidence interval for the relative risk can be correct. The more
imprecise their measure of pre-war mortality, the worse this conflict becomes.

It seems to be that either a) I don’t understand what is going on or, b) there is something fundamentally wrong with the results. Which is it?

Thanks for any help that your readers (or you!) can provide.

My quick thought is that new data became available between 2004 and 2006. The 2006 paper cited in my earlier blog entry estimated a pre-invasion mortality rate of 5.5 and a post-invasion rate of 13.3 (with confidence interval of [10.9, 16.1]) which is different from the [1.4, 23.2] interval you have above.