For some things there are specifics. We know for example, that between 2003 and 2014, 4,497 US troops lost their lives in Iraq.
And we also know that 179 British servicemen and women were killed, in the period until UK forces withdrew in 2009.
But when it comes to the Iraqi death toll - civilians, soldiers, insurgents, the lot - things are a lot more hazy. And the US government claimed, infamously, it did "not do body counts".
There have been estimates, calculations, counts of casualties reported by the media. But 13 years after the US and UK invaded, one of the greatest tragedies of the horrors that played out in those bloody years, is that we still don’t know how many Iraqis died because of actions carried out in our name.
One of the first groups to try and come up with a number was the Iraq Body Count, a British project that maintained a tally of casualties based on media reports.
The project currently lists the number of civilian deaths at between 160,400 – 179,312, with a total of violent deaths including combatants at around 251,000. But as the IBC has admitted, its figures are based on reports in the media, which were themselves limited in scope and detail, especially when the conflict was at its deadliest.
Others have used extrapolation based on epidemiology. Two reports conducted by the Johns Hopkins University’s Bloomberg School of Public Health, were published in The Lancet. The first, published in 2004, estimated that at least 100,000 Iraqis had been killed as a result of the war.
The second, published in 2006, suggested that the figure had risen to near 650,000. The British and US governments, along with some independent experts criticised the reports, but but those involved, and The Lancet, defended the methodology.
Last year, a report by Physicians for Social Responsibility suggested the total may have passed one million.
One of those involved in The Lancet reports was Les Roberts, Professor of Population and Family Health at Columbia University. He said on Tuesday that one of the most important reasons for the lack of a precise total, was that the US and UK governments had actively tried to avoid such a figure being made available.
Another powerful factor, he said, was the role of the media in failing to report on uncomfortable truths. “I think much of the cover-up comes from the press,” he told The Independent. “The press is very rarely willing to cover something that goes against the public will. And up until 2005, the general public was largely in favour of Iraq.
Yet, Mr Roberts said he believed that a consensus about the rough number killed in Iraq - one that put the death toll well over 500,000.
“I don’t think we learned the lessons we should have,” he said. “The report today today raises these issues. I would hope everyone would say ‘This has been a disaster - don’t let it happen again’.”
Another person still seeking answers about the number of people killed in Iraq - and in pushing for justice for those responsible - is Cindy Sheehan. Ms Sheehan's son, Casey, was among the US military casualties to lose their lives in Iraq and in August 2005 she created international headlines, when she set up a makeshift camp outside Mr Bush’s Texas ranch to demand a response.
Speaking from her home in California, she said the publication of Tuesday’s report, underlined what many anti-war protesters had already known - that the invasion was planned and intended. It was not as if the US and UK had “stumbled into action”.
“Every day I live with this devastation,” she said. And she said it was not just her - there were countless others both in the US and Iraq whose loved ones lost their lives, or in the case of the Iraqis, been forced to flee their homes. Today, she said, Iraq was a clear disaster. Just on Sunday, a huge bomb blast, blamed on Isis, killed more than 200 people in Baghdad.
She added: “With Tony Blair, the thing that hurts the most, is that he says he is very sorry, but that he still thinks it was the right thing to do.”
She said she was trying to honour her son’s memory by speaking out about what happened, remembering the dead - whose precise number we may never know - and working to ensure such events are not repeated.
“If I can stop anything like this happening again,” she said. “I will be honouring him.”
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