Responsible bar charting

Of all the voting systems, first past the post in single-member constituencies particularly incentivises tactical voting. That can be for positive reasons – such as a voter really wants to elect a candidate who will prioritise environmental polices – or for negative reasons – such as to try to defeat a party the voter really dislikes. Either way, it’s up to the voter to decide what matters most to them and to act accordingly.

Of course, political campaigns can legitimately try to influence each stage of that – including how best to turn your views into an effective vote. Which is where, since the 1970s, the bar chart comes in…

Research shows both that the choice of bar chart (rather than, say, pie chart) is the right graphical device and also that the underlying political message can work.

Moreover, there is no one definitive source of information about who is the best tactical voting choice in a seat that is always, without doubt and without fail, in all seats and for all time, correct.

Politics, for example, can have changed significantly since the previous election of the same time. There is scope for legitimate disagreement on this, just as on much else in politics.

There’s no need to jump the moment an opposition activist complains. (And those currently insisting that the 2017 results are complete gospel with any more recent information 100% irrelevant, are not exactly making a convincing case.) Even so, there are better and worse ways to make a tactical voting argument with a bar chart.

How, then, to make a case effectively using a bar chart?

  1. Get the heights right. It should be a source of self-pride to be millimetre perfect.
  2. Give the source of the data you are using.
  3. If using polling, be clear to distinguish between a constituency poll, modelled results (such as MRP) or figures extrapolated from regional or national polls. All can have their place, but don’t use one and stick a label on suggesting it’s another.
  4. Title the bar chart and add explanatory text: you may know why the bar chart is there; I may know why the bar chart is there; but for a voter not so used to paying attention to politics…?
  5. Don’t think a bar chart alone is enough to make the tactical voting case: you need plenty of other supporting material, such as a good poster display, a more intensive leafleting schedule than other would-be recipients of tactical voting and regular stories such as about growing local party membership.

Get that right, and bar charts can be a valuable part of a winning election campaign.

I also talked about this topic in an interview with The Pod Delusion podcast, which you can listen to here.

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