Then how is it a very accurate study? How can anyone difinitiy say the number was 500k?
Ah shit, I just wrote a long response to this but accidentally lost what I wrote by double-clicking in the preview pane.
Anyway, depends what you mean by an "accurate study". The study is accurate in that it's very upfront about how sure (or not) one can be about its results.
No one can definitively say what the number (of Iraqi deaths attributable to the USA's invasion of Iraq) is and that's why the study's authors present its results as "460,000 deaths with a 95% confidence (or uncertainty) interval of a (whopping) 48,000 - 751,000 deaths".
(It's also important, btw, to understand what the study is talking about when it says "attributable" but they pretty clearly lay that out.)
So what's the value of this study? Here's the money paragraph (for me):
What Do These Findings Mean?
These findings provide the most up-to-date estimates of the death toll of the Iraq war and subsequent conflict. However, given the difficult circumstances, the estimates are associated with substantial uncertainties. The researchers extrapolated from a small representative sample of households to estimate Iraq's national death toll. In addition, respondents were asked to recall events that occurred up to ten years prior, which can lead to inaccuracies. The researchers also had to rely on outdated census data (the last complete population census in Iraq dates back to 1987) for their overall population figures. Thus, to accompany their estimate of 460,000 excess deaths from March 2003 to mid-2011, the authors used statistical methods to determine the likely range of the true estimate. Based on the statistical methods, the researchers are 95% confident that the true number of excess deaths lies between 48,000 and 751,000—a large range. More than two years past the end of the period covered in this study, the conflict in Iraq is far from over and continues to cost lives at alarming rates. As discussed in an accompanying Perspective by Salman Rawaf, violence and lawlessness continue to the present day. In addition, post-war Iraq has limited capacity to re-establish and maintain its battered public health and safety infrastructure.So while it seems that any study for the specific purpose of determining the actual number of Iraqi deaths attributable to the USA's invasion of Iraq will be of only limited value, the study IS valuable when trying to find the answer to the more important question, "Did the USA's invasion of Iraq destroy the lives of a huge number of Iraqi people?"
The answer, of course, is "Hell yes!"... and no American should be proud of that.