Home > Commentary, Maths, Strange, Teaching > Statistical Deception

## Statistical Deception

When teaching and talking about statistics I always emphasise the need to be careful what you believe and to always ask yourself “what agenda does the person presenting this data have?”

I’ve written before about how stats can legitimately be manipulated to serve different points of views, especially when there are false variables at work. But recently I’ve noticed at darker art in statistical manipulation, one that is, at its heart, lying.

We are less than six weeks away from local elections now, and it is becoming silly season for party political leaflets coming through our letterboxes. Now we all know that the political parties will present data in a way that makes them look better, they are trying to win your vote afterall, but we would expect them not to lie. For the data to be accurate and presented correctly. Unfortunately, however, this is not always the case:

Exhibit A

This popped up a number of times in my twitter feed from a variety of sources. I believe it is from a Lib Dem leaflet in Manchester. As you can see, they have presented a bar chart with proportions labelled as percentages. The first screaming error is that the red bar and the orange bar are massively different heights, yet are both emblazoned by the label 39%. The second glaring error is that the percentages add up to more than 100%. The first implies that either the Lib Dems are deliberately trying to mislead voters into thinking they are in a stronger position in the ward than they are, or that they don’t realise that 39% is equal to 39%. I’m not sure which is worse?!

Here’s an excel interpretation of what the graphs should look like:

Exhibit B

This graph came through my door in Leeds North West parliamentary constituency. The first thing that caught my eye was that although the gap between the number of votes between Lib Dems and Labour; and between Labour and Conservative is almost the same, the difference in the gaps between the bars was almost 5 times as big, which would imply almost five times as many less votes! An obvious fallacy. Either it’s a deliberate attempt to mislead, or they can’t draw a bar chart. If it’s the latter, do we want them in charge of our local authority budgets?! (or the entire economy for that matter!!)

Something else that struck me as deciving, although this time mathematically correct at least, was the choice of data. This was a leaflet issued in the run up to a local election, and the data set used was from the last local election. Why then, is the data that for the parliamentary constituency rather than the council ward? The ward makes up around a quarter of the constituency, and the vote share in the ward is radically different to that of the constituency. The sitting councilor is conservative and sits on a huge majority, and the Lib Dem candidate last time out cane third. To issue a leaflet in the run up to a local election which implies the conservatives can’t win in a ward where they have a large majority and back it up with local election data for a parliamentary constituency is deliberately deceptive and misleading.

Here’s an excel interpretation of what this one should look like:

Exhibit C

This one comes from “across the pond” and is another which was viral. This one seemed to appear constantly for a few days everywhere I looked. If you are still wondering what’s wrong with it, take a little look at those numbers down the left hand side…. See it? The y axis goes upwards to zero! Drew Barker (@twentythree) made this version which gives a much better picture as to what’s going on.

I can’t wait to see what my classes make of these!

nb I haven’t “selected” these graphs as an attack on the Lib Dems, it’s just they are the only party who have sent me a leaflet with incorrect maths. I’ll gladly expose any of the parties if they themselves do. I do collect these, so if you spot anything similar, do send me it!

Categories: Commentary, Maths, Strange, Teaching
1. April 21, 2014 at 6:50 pm

Reblogged this on The Echo Chamber.

2. April 22, 2014 at 7:34 am

One of the things that I’ve wanted is for anyone quoting a figure (e.g., 34% of blah blah; we now have 7 million new users; etc) to provide a link to the raw data used that has been “verified” by some independent third party as being authentic data. In addition to pointing to the data used, I also want a mathematical explanation as to how the final result was computed. These two things would make it abundantly transparent if there is any chicanery.
The graphs presented are, well … I have no kind words.

• April 22, 2014 at 9:56 am

Aye, I totally agree. We need more transparency in these matters

3. April 22, 2014 at 8:58 pm

ALL of the dodgy political graphs I use with my classes come from the Lib Dems here in Woking. They seem to have a national strategy for dodgy graphs. One exception: a Tory manifesto graph that omits 15 out of 25 EU countries to make it look like Britain is in last place!

• April 22, 2014 at 9:07 pm

Yes, the Lib Dems do seem to have a blatant disregard for correct graphs, and you know, the truth! But there must be other examples… I’d love a copy of the EU graph!

1. May 3, 2016 at 9:47 pm