How to make a political graph properly

Pie chart of govt spendI appreciate that the title of this blog post may be a hostage to fortune and I may be called out on my attempt to produce a graph properly. But given I’ve called others out on poor graphics I thought I ought to put my money where my mouth is.

Someone posted this graph on my Facebook page and said “no attribution but what do you reckon?”

The original Facebook post of the person who initially posted this chart said “What the UK spends its money on.  If you look very hard, you’ll spot EU membership in there somewhere.”

So, rather than just say it was a badly chosen chart produced in an uneasy to decipher way (which it is), I thought I’d have a go at making this chart better. I should add I may not be using exactly the same data as the original chart as I don’t know where the author got it from (edited to add: see footnote as the original data soruce is now known). But for your info I am using the government’s Public Expenditure Statistical Analysis 2014-15.

So why do I think this was a badly chosen chart? Well, it’s a pie chart and pie charts are nearly always bad charts to use. So what’s wrong with pie charts?

Let’s take a step back and ask ourselves “what is a chart or graph?”

Technically speaking it is the visual display of quantitative information. Incidentally this is the title of a massively influential data visualisation book by Edward Tufte.

Any chart encodes a numerical value visually, for example, as a plot on an x-y graph, as a bar in a bar chart or as a slice in a pie chart.

In a bar chart the numerical value is encoded in the length of the bar.

A pie chart seeks to show the relationship of each slice to the whole, effectively showing the percentage of the whole.  In a pie chart percentage value is encoded in the internal angle of the pie slice.

The issue here is that charts ad graphs are used to compare values and it is far easier to compare by eye the lengths of a bar in a bar chart as oppose to the internal angles of spices in a pie chart.

But sometimes pictures can tell the story better than words. Take a look at the two pictures below.

Bad pie 2

Bad pie 2

The above examples were borrowed from here. There you go:  bar charts are (nearly always) better than pie charts.

So now let’s see how we can improve upon the original pie chart. Note I’ve not used exactly the same data so I done a rough reproduction of the original chart below. As you will see while it is not a busy and hard to read as the original it is still not easy to read and do comparisons across the spend types.
Pie govt spend - ravi
Just for a laugh let’s see it in 3D. You will see adding 3D makes it even more difficult to read accurately as the 3D effect now distorts the way the internal angles are viewed. Never, ever, ever use 3D pie charts. They are the enemy of clarity and understanding.
pie 3d
So let’s turn it into a bar chart instead. See below. You can see it is far easier to compare the spend on each item as all you have to do is quickly compare the bar lengths, which is far easier than comparing pie slices/angles.
bar govt spend
The above bar chart is better, but we can still improve upon it by turning it into horizontal bar chart so the labels are easier to read. And to make it even better, we should order the bars from largest to smallest; add titles; makes the grid lines less dominant; and add a reference to the author and where the data came from.
horiz bar

I once was the one of the view that pie charts should never be used but I’ve softened a little and I think very occasionally pie charts can be used to illustrate data clearly. I’ve knocked up a pie chart to illustrate this point.

Note, just to amuse myself, I could not help myself but to colour it yellow and rotate it to produce a Pacman type chart.

good pie
There you go folks. It is possible to make your point quickly and clearly if you chose the right chart and think about how you present the data.

On the actual issue of EU membership I’m firmly with the remain camp. My reasons for supporting remain are perhaps best summed up by my union’s General Secretary Dave Prentis who recently gave three good reasons for suppporting remain in his blog:

Rights at work – the regulations we rely upon to protect people at work are enshrined in EU law and upheld by the European Court of Justice. Leaving would mean that hard-won rights like paid holiday, fair working hours, equal rights for part-time workers, and maternity and paternity leave would no longer be guaranteed.

Protecting your standard of living – leaving the EU would put working people’s standard of living at risk by creating economic uncertainty. This would risk investment in jobs and damage consumer confidence. It would also make the pound vulnerable, which would push up prices and interest rates.

Protecting public services – we see every day how a weaker economy has meant cuts in public spending affecting everything including the NHS, local services, policing and education. We can’t afford to risk any more cutbacks at a time when our public services are under increasing pressure.

To read his full blog post on why UNISON are campaigning to remain go here.

Edited to add: Since tweeting this post out I’ve been informed that the original pie chart came from this blog and the source data was the Public Expenditure Statistical Analysis of public spending in 2013-14. My source s the same but for the more financial year 2014-15.


5 thoughts on “How to make a political graph properly

  1. Pingback: Pac-Man pie chart of UK’s spend on the EU | More Known Than Proven

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  4. Pingback: Pie chart to show how Brexit will weaken our trading power | More Known Than Proven

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