Dear Mark Thompson and Will Straw,
I read your joint blogpost last week on Mark Reckons and Left Foot Forward about whether the MPs with the safest seats are the worst expenses claimants with some interest. The original suggestion of a link came several months ago on Mark’s blog and it certainly provoked discussion in various political channels. However, on looking through your analysis and doing my own version, I find it very hard to agree with your conclusions.
I’ll start with a quick recap on your main analysis:
“…in order to try and find a better way to see if the safety of an MP’s seat could be correlated with the amount of expenses money claimed we listed the 328 MPs who (after appeals and adjustments) have been asked to pay money back and ordered them by size of payment. This way we are now taking into account this wide range of difference in amounts paid back and including all the implicated MPs.
We then split this data into quartiles and looked at the average size of the majority for the MPs in each quartile. What we found is that for MPs in the top quartile (including Barbara Follett, Andrew Mackay, and many of the most controversial claims) the average majority is 8,678. In the second quartile the average majority is 7,534. In the third it is 7,705. And in the lowest quartile (including people like Mike Gapes and his 40p) the average majority is 7,276. So there is a fair bit of difference here but there is another point to note. The average size of majority for all 328 MPs implicated is 7,798 (7,613 for all MPs). This means that the top quartile is quite a way above this average (by nearly 1,000 depending on from which point you measure it) and the bottom quartile is a fair way below it (by close to 500). The two middle quartiles are clustered near the average(s).
As with Mark’s original posts, there will likely be debate over what these figures tell us the degree of statistical significance, but we feel that, at the margin, they show that there is a link between the expenses scandal and the size of an MP’s majority. Of those MPs implicated, on average the safer their seat, the more they wrongly claimed.”
Sorry, don’t buy it, and here’s why.
First, I find it extremely hard to understand why you are only discussing MPs who paid back expenses in this analysis. Your conclusion is that there is a link between the expenses scandal and the size of an MP’s majority, yet you explicitly excluded every MP who didn’t cheat on their expenses from your statistical analysis. What’s up with that?! If it is indeed true that the MPs with the safest seats were the biggest cheats, surely, you cannot just cut out all the MPs who didn’t cheat at all!
Second, the use of quartiles and lumping MPs who paid money back into big groups doesn’t seem that helpful. What you need to show is a clear, unambiguous pattern between your two variables and I don’t think this type of data really tells you much.
So here is my contribution to the debate. Instead of excluding MPs who weren’t caught cheating, I’m going to look at all MPs because this is the only way to definitively identify a link between safe seats and crooked politicians. In addition, I’ve chosen a scattergraph and subsequent correlational analysis to look for clues. And here’s what I got:

The first thing you’ll notice is that the majority of MPs who paid nothing back is sizeable, hence the blue blob at the bottom of the graph. I’m sure it would look very different if only MPs who had actually paid money back were included but, like I said, to establish a link between the safety of an MP’s seat and their propensity to cheat the expenses system you must include everyone.
Not only does the pattern that you claimed seem to disappear from visually inspecting the scattergraph, a correlational analysis shows that link is a mere 0.05, which is about as close to ‘no relationship whatsoever’ as you can get. I noticed that Mark carried out a Spearman’s Rank correlation test and found a “weak positive correlation” between the two variables, but this was only for MPs who had paid money back, which I don’t think is a valid test.
So there you have it: a totally amateurish Excel-powered debunking of the myth that MPs with the safest seats were more likely to cheat on their expenses. Over to you, gents.
Regards
A.Tory
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