The year in figures: numbers have a curious power over us: orators, from high-school debaters to candidates for high office, know persuasive appeals gain credibility if seasoned with data.

Sometimes numbers cast a wicked spell. Charles Seife, author of Proofiness, points to Senator Joseph McCarthy’s “list of 205” known communists working in the State department. This figure, which he later reduced to 57 for no apparent reason, was untrue. Yet without its rhetorical power, McCarthyism would probably never have infected the US body politic. Readers of this newspaper are, we hope, spared the worst of such fabrications, but I can assure them that in 2010 they have been alive and thriving beyond these hallowed pages.

More accurate statistics may still serve a rhetorical purpose: as punctuation. We already knew BP and its contractors should have been more careful when drilling the Macondo oil well. The realisation that BP lost 340,000 times what it saved by not running a particular test throws that information into sharp focus.

But, at their best, data tell us something new: at about $400m a day, the cost to the entire airline industry of the ash cloud emitted by Eyjafjallajökull, the Icelandic volcano, was strikingly similar to the cost of the Macondo spill to BP alone. The difference, as BP shareholders will attest, is that the cloud grounded flights for just over a week, while the spill dragged on for three months.

At times the headlines are out of all proportion to the data. The 11,041 deaths in the Mexican drug war is a truly astonishing statistic for an often under-reported story. They have been overshadowed by the 948 hostages taken by Somali pirates. And both, of course, were drowned out by the uplifting and telegenic story of 33 men trapped underground for 69 days in Chile.

China’s rise has been marked by one long-anticipated statistical milestone: its economy is now larger than Japan’s. Looking over the decade, though, the more striking change has been the integration of India, which started from a far lower base, into the world economy.

A final warning: even when numbers are calculated in good faith and pored over by experts, they can deceive. The estimate of the UK government’s budget deficit for 2010-11 has fluctuated – from £26bn in the pre-crisis Budget of 2007; to £183bn at the beginning of 2010; to the latest Office for Budget Responsibility forecast of £145bn. For reference, the budget of the National Health Service is a little over £100bn. If you want to know the true deficit for 2010-11, you will have to wait until this time next year.

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