Facts and data - and fibs about them

Full Fact fails to spot Jeremy Corbyn’s dishonest data picking first time

I have a lot of time for Full Fact, the independent fact checking charity. We need them.

Yesterday though they cocked up and fell for one of the oldest tricks in the book – it is called data picking. Choosing the data to suit your argument. We all do it to some extent but you can usually spot it, or stop yourself doing it, if you look at the wider data to see if the factoid being pushed at you is reasonable or relies on a quirk in the data.

On Wednesday at Prime Minister’s question time Jeremy Corbyn came out with a dishonest factoid that was based on just such data picking. He said:

The amount of tax paid by the super-rich in income tax has fallen from 4.4 billion to 3.5 billion since 2009.

Oh dear you might think. Killer factoid. The Tories are bang to rights. Well, no.

Unfortunately yesterday Full Fact fell for Corbyn’s trick and they pushed out a piece that said, yes, he was right and tweeted this link to it at 11.05am with a graphic, since withdrawn.

As soon as I saw the tweet I knew exactly the trick that had been played. The data had been distorted by changes to the highest rate of tax, 50% on incomes over £150,000, introduced in April 2010. And then reduced to 45% in April 2013. Wealthy individuals took their income in 2009/2010 rather than 2010/2011 to benefit from the 40% rate. Hence the tax take dropped from £4.4 billion to £2.8 billion. The opposite happened three years later when the rate went back down to 45%. People deferred their income which meant the tax take went up from £2.6 billion to £3.9 billion. You can see the effect of the rate changes quite clearly in the chart below. The tax take from the wealthiest is creeping up.

£3 billion in 2011/2012.
Average of £3.25 billion the next two years.
£3.5 billion in 2014/2015.

To their credit Full fact withdrew their earlier piece and replaced it with one that was much more fact-ey. Well done. Beware of data picking.