What’s wrong with this graph?

indy-ref-by-ageIt’s been niggling me since the result was announced, but there were other things to do, so it took me a few days to sit down and scratch this itch.

The headline is simple. Older voters defeated the Scottish independence referendum, as illustrated by this graph breaking down voter intentions.

But data journalism can be a tricky thing, and graphs can easily misleading unless designed with a bit of thought. Take a look at the first bar. It illustrates the voting intentions of 16 and 17 year old voters. A two-year gap. Then there’s 18-24, a seven year group. Then ten-year steps until we reach 64, then “65+”.

Now look again. There’s no information about varying turnout rates, and even with 84% overall voting, I’m willing to bet turnout increased with voter age. Yet there’s a graph that gives the visual impression that over 65s (a cohort that covers a 30-40 year age range) is the same size as one for 16 and 17 year olds.

The graph, whether intentionally or otherwise, gives the impression of a small minority overruling the wishes of a majority.

And that annoys me.

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  1. Actually it’s worse.

    The figure of 71% 16-17 year olds voting YES comes from a poll conducted by Lord Ashcroft. His sample was 2000 people. HOWEVER only 14 of these respondents were aged 16 or 17. So the claim that 71% of 16-17 year olds voted YES really means than 10 out of the 14 young people polled by Ashcroft said they voted YES.

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