A few bad apples — or a cartload?

June 2, 2009

Tom Whipple
387 words
26 May 2009
The Times
(c) 2009 Times Newspapers Limited. All rights reserved

While using taxpayers’ money to pay for dredging of moats and duck ponds may tell you something about individual MPs, it is difficult to deduce anything broader about the state of the Commons from such stories. To see what really went on, we need numbers.

In the past two weeks, second-home expenses claims of more than 100 MPs have been broken down and published. Many as-yet-untarnished MPs claim that the House has been let down by bad apples. Statistically, they are arguing that there are two expenses populations: the crooked and the clean. Some of the accused MPs make the counter-claim that they are just unlucky; that they follow the rules in the same way as all 675 MPs. Statistically, they argue that there is one MP population, made up of the crooked … and the caught.

There is a way to test this. Parliament already publishes the second-home expenses of every MP, without individual breakdowns. So we have always had data for the whole MP population. Now we can also identify a subset whose expenses, broken down, look dodgy. The question is, do these sets, as the untarnished MPs claim, act differently? Do the dodgy MPs spend more? A crude way to test if two sets of data are similar is to see if they share the same average and variance, which is the movement about that average.

For all MPs, the average second-homes claim was £16,500 in 2004 and £18,000 last year. For those MPs whose expenses claims have been criticised, the average claim is £1,500 above that. The variance is also different. It seems that the “crooked and clean” hypothesis should be accepted.

But the expenses furore concentrated on second-home allowances — so only those who could justify second homes were scrutinised. As the overall MP population also includes those with no second home (who claim £0), we are not comparing like with like. What if we remove those 50, mainly London-based, MPs? Then the average rises by £1,500 and the variances equalise. The populations are the same, after all.

Does this mean that all MPs are equally corrupt? Or uncorrupt? That, alas, is as far as the numbers will take us.


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