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Pedants' corner

Pie charts

52 replies

DadDadDad · 09/11/2015 22:29

Not a language peeve for once, but still a point for pedantry. What is wrong with this picture? (Not the made-up data - that's me trying to be funny - but what's wrong with the way it's presented).

Pie charts
OP posts:
StealthPolarBear · 09/11/2015 22:32

3d charts generally frowned on
pie chart generally frowned on
no numbers you can't really tell the relative proportions - it doesn't do its job of delivering the message

StealthPolarBear · 09/11/2015 22:33

Mil or parking could be top

StealthPolarBear · 09/11/2015 22:34

But we all know it's really threads askin about your favourite mners

And what about overlaps. Eg your mils poor parking and shocking grammar

StealthPolarBear · 09/11/2015 22:34

Why do I have to click post twice. Really irritating.

FlapSnaps · 09/11/2015 22:37

Yes we need percentages. And lose the 3D effect - maths is beautiful enough without requiring decoration. Even if it is a pie chart.

elephantoverthehill · 09/11/2015 22:41

No time frame when the data was collected, how the data was collected. No actual figures or percentages. What was the point of the data collection. I'm sorry I'm tired. And no X or Y graph titles. It does not really show any comparison.

DadDadDad · 09/11/2015 22:49

All good points. As I said, don't focus on the data, more the format. But, it's the use of a 3D view that really gets me irritated, and you see it all the time. In fact, I can't think the last time I saw a non-3D one!

The one thing that a pie-chart conveys (as opposed to a bar-chart) is relative proportion. In theory, if there are no numbers on the chart, it's still meaningful as you can whip out a protractor and find for yourself the percentage for each category. But as soon as you make the view 3-D, you lose that one piece of information, ie YOU BREAK THE PIE-CHART! Sorry, not shouting at you clever people, just the marketeers and finance show-offs who haven't grown up from when they were ten, and 3-D pie-charts looked cool. Angry

OP posts:
DadDadDad · 09/11/2015 22:51

Sorry, I should have acknowledged that some posters said the 3-D view is a no-no.

Can you tell from my picture whether parking is more or less than a quarter of the total?

OP posts:
elephantoverthehill · 09/11/2015 22:59

I think, though I am not sure and can't be bothered to look it up that Florence Nightingale introduced the pie chart. I totally get your point about protractors.

PurpleDaisies · 09/11/2015 22:59

It looks almost exactly a quarter of the total to me. I don't think there is necessarily a huge problem with using 3d pie charts if there are percentages attached to the different categories. I'd always use a flat pie chart but isn't it more a question of style rather than one being absolutely incorrect?

DadDadDad · 09/11/2015 23:00

I think I read that's a bit of a myth about Nightingale, although she was a big proponent of statistics and may have used pie charts. Maybe someone should read up on Wikipedia, because I think it's covered there.

OP posts:
senua · 09/11/2015 23:00

I see what you mean - perspective means that we can't tell at a glance whether the red section really is big or just appears big.

However, newspapers usually give us:

  1. the pie chart
  2. the figures
  3. the percentages
  4. a talk-through of the numbers again in the article not that they are trying to fill column inches, oh no
    so we can usually work out what is going on.
DadDadDad · 09/11/2015 23:04

Purple - I'd say it's more than a question of style. If I show you the flat version, you can see much more clearly that Parking is 25% of the pie chart. You can also see that Bad grammar and Other are the same size. If you are going to show information visually (rather than just a table of percentages) why destroy the one thing that a pie chart accurately conveys?

Pie charts
OP posts:
SenecaFalls · 09/11/2015 23:07

And what about overlaps. Eg your mils poor parking and shocking grammar

Oh, I do love a nice Venn diagram. Smile

PurpleDaisies · 09/11/2015 23:08

Not to blow my own trumpet too much but I deduced all those things correctly from the 3d pie chart Wink.

MsMermaid · 09/11/2015 23:08

I had this exact conversation at work yesterday. Are you my head of department?

We even included Florence nightingale in the conversation (she didn't invent it, but she is credited as popularising it)

PurpleDaisies · 09/11/2015 23:10

There are never enough Venn diagrams in everyday life for my liking seneca.

StealthPolarBear · 09/11/2015 23:10

No she didn't invent it that was monsieur pie. Also credited with the chicken pie and lemon meringue pie.

DadDadDad · 09/11/2015 23:11

This is an unbelievable coincidence, but I just had the Daily Mail website open (yeah, I know, shoot me), and they have an article with a pie-chart. They've avoided the 3D trap, but instead put themselves forward for the award of most ridiculous use of a pie chart!

Have a look yourselves.

Ha! If I bought four cups of coffee, one each from these establishments and mixed them in a cup, this pie would usefully show how the proportion of caffeine is split between the 4 cafes. But, that would be silly. Shock

A bar chart showing the amount of caffeine would be much more meaningful enabling me to directly compare any two cafes, see which gave the most etc.

Pie charts
OP posts:
StealthPolarBear · 09/11/2015 23:12

That is a stupid stupid pie chart

MsMermaid · 09/11/2015 23:13

I have far too many Venn diagrams in my life. Never used properly, because the man who produces them and lectures us about the data involved doesn't seem to fully comprehend what they're for

MilkTwoSugarsThanks · 09/11/2015 23:14

You do know that you can change the angle of a pie chart so it can still be 3D while still showing (more?) accurate proportions, don't you?

(The proportions looked fine in your first 3D chart tbh)

DadDadDad · 09/11/2015 23:15

Purple - but it's not possible to deduce those things from a 3D chart. You may persuade yourself that you can see that, but it would be difficult to prove it even if you took measurements from my original picture. (I suppose, if you got the dimensions of the ellipse and did some fancy geometry it might be possible, but that's a lot of work!).

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PurpleDaisies · 09/11/2015 23:20

I'm sorry to disagree but I really did get those proportions from your original pie chart. I don't think I'm a mathematical marvel. I agree you can't get the precise percentages but that's solved by adding those on.

mammmamia · 09/11/2015 23:31

That pie chart is ridiculous

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