THE fog of war frustrates statisticians: knowing for sure how many Syrians have died can seem as difficult as brokering a lasting peace. The last precise death toll published by the UN was 191,369 in August 2014, followed by an estimate of more than 250,000 in August 2015. But it then stopped updating the figure because of dwindling sources of good information. On February 11th the Syrian Centre for Policy Research (SCPR), a non-profit group, claimed that the true figure is now almost double that estimate at about 470,000.

This number may seem large, but even the UN emphasised that its figures were conservative. It erred on the side of rigour rather than completeness, and only counted people whose names it knew and whose deaths were confirmed by more than one source.

Extreme conditions have forced more approximate approaches. The SCPR divided Syria into 700 regions, and asked three local experts in each to give detailed information. If one gave an answer more than 10% apart from the others, they were replaced with two different “informants”. Rabie Nasser, an author of the report, says resampling happened in only about 10% of cases. The figure of 470,000, which comes with a 5% margin for error either side, is the sum of the average answers across regions.

Relying on people to estimate the body count in large areas rent by civil war is bold. All sorts of biases could have crept in, not to mention the risk that the “informants” will have tweaked their figures to suit their own political agenda (though Mr Nasser says his team tried to find independent sources).

Nonetheless, 470,000 could be close to the true figure. Since mid-2015 Russian bombs have added to the casualties. And whereas the UN figure only included deaths directly caused by fighting, the SCPR figure includes indirect deaths (about 15% of the total). The war has blasted hospitals and ruptured supplies of clean water, allowing disease to spread. Over time, Mr Nasser expects indirect deaths to climb as a proportion of the total.

No one really knows how many have died in Syria; the 470,000 figure is only one estimate. The UN’s approach is that with such decay in the underlying data, it is better to be cautious than to risk losing credibility. Mr Nasser takes a different line. “If you’re in a conflict where people die, then you don’t give up.”