Lies, Damned Lies, and Statistics (And Ash Clouds)

Willie Walsh from British Airways was on the Today program this morning complaining about restrictions on flying and volcanic ash. To illustrate his point he brought along 4g, or about a teaspoon, of ash and pointed out that they were not supposed to fly in concentrations of 4mg per cubic meter. One thousandth of his teaspoonful in one cubic meter of air. He said “We really are talking about tiny amounts of ash”.

My point is not to support either side of this debate. My point is that these numbers, out of context, are utterly meaningless. Let’s look briefly at some more numbers.

A modern jet engine shifts about 1.3 tonnes of air every second! Enough to fill the Goodyear Airship in less than ten seconds. This means that each engine on your plane has to swallow about half a pound of ash every minute – and keep working. Doesn’t sound like such a “tiny amount of ash” now does it?

Numbers out of context are constantly appearing in bad science reporting, usually in a medical story. How many time have you heard something like Eating too many eggs/sausages/steaks/curries can increase your chances of getting cancer/heart disease/alzheimer’s  by 50%

This is meaningless without the context: How many is too many? What are you chances of getting the disease anyway etc. Etc.

Even if the 50% figure is true, then if you have a 1 chance in 100,000 of getting disease X anyway then you are only increasing those chances to 1.5 chances in 100,000. Not so scary now is it?

As a real world example :

“600 pregnancies despite contraceptive implant” said the BBC. “500 fall pregnant after having contraceptive implant” said the Express. “Contraceptive implant alert” said the Daily Mail: “Hundreds of women fall pregnant after birth control fails”.

This story broke earlier this year on Channel 4 and was about a contraceptive implant called Implanon. What none of the reports mentioned was that there were about 1.3 million of these sold. A good estimate for the failure rate would be about 0.014% per year. This makes it just about the MOST effective contraceptive available!

Numbers out of context are at best meaningless at worst deliberately misleading. Whenever you see or hear numbers in a report YOU have to stop and think about what they really mean, because I’m afraid those being interviewed almost always have an axe to grand and the interviewers rarely have the knowledge or the skill to challenge them.

Incidentally I have a method which will increase your chance of winning the National Lottery by 200%. Put three lines on instead of one your odds improve from 1 in 14,000,000 to 3 in 14,000,000.

Don’t hand in your notice just yet eh!

Click for a hilarious take on the subject by Tim Minchin (Sorry this link doesn’t work any more. the song is called “Context” go find it – you’ll love it)

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