Jeremy Laurance: Cameron's cancer figures could do with a check-up

Whenever politicians quote statistics, it is time to reach for the Rule of the Lesser Miracle, devised by the 18th century philosopher David Hume to test the veracity of biblical claims about the doings of Jesus Christ. I was reminded of this when David Cameron claimed in the party leaders' TV debate that Britain's death rate for cancer was "actually worse than the Bulgarians'". Could that be true?

Hume's argument was that a rational man would always believe the lesser of two miracles. In the case of the claim that Jesus walked on water, for example, which is the lesser miracle: that he did so or that the disciples were deceived? Applying the rule to Cameron's claim, which would be the lesser miracle – that Britain's NHS has a worse record for cancer survival than Bulgaria, or that Bulgaria is less reliable at collecting cancer statistics than Britain? Eurostat health data for 2007 does indeed show that Bulgaria had 170.3 cancer deaths per 100,000 population whereas the UK had 178.1 deaths. Cameron chooses to see this as evidence of Britain's dismal performance.

But it is the very fact that the figures show Britain performs worse than Bulgaria that calls the data into question. They defy belief, but Cameron chose not to question them but to accept them at face value. Britain's cancer registries are among the best in the world and the reason we appear to have more deaths than some less advanced countries is because we are better at counting them.

But we are not alone. Bulgaria's overall cancer death rate, as Labour pointed out, is lower than the USA, Belgium, Canada, Denmark, France, Germany, Ireland, Italy, the Netherlands, New Zealand and Austria. Nor is Bulgaria alone. According to World Health Organisation figures the following countries can celebrate lower cancer death rates than the western nations mentioned above: Algeria, Azerbaijan, Bangladesh, Colombia, India, Iran, Libya, Morocco, Namibia, Saudi Arabia, Ukraine, Uzbekistan, the Yemen, Belize and the Democratic People's Republic of Korea. I look forward to the day when, under a future Tory government, NHS patients begin demanding cancer treatment in Bangladesh because of the poor quality of services back home.

One reason why cancer kills more people in the West is because, thanks to high standards of medical care, they live long enough to get it (cancer is principally a disease of old age) rather than dying of something else. This is not to say that Britain's cancer record is excellent. It is far from being so. Our survival rates are poor compared with Europe and up to 11,000 deaths could be prevented every year if survival rates were at the levels of the best-performing countries, according to a report last year.

The Tories blame lack of access to the best new cancer drugs. But evidence suggests it is patients being diagnosed and referred late that is a bigger problem. Either way, the use of shoddy statistics is no way to conduct a debate about Britain's most important public service.