In praise of the ‘Don’t know’ voter

I am scraping the edges of my memory here, but I am fairly sure that opinion polls in my childhood (for the elections of 1970, 1974 and 1979) quoted four percentages: Conservative, Labour, Liberal and ‘Undecided’. Nowadays no figure is quoted for ‘Don’t knows’, and party support is contrived to add up to 100 per cent. Undecided respondents are variously treated according to each polling company’s methodology: a few ignore them completely; others apply a supplementary question such as ‘Which way would you vote if voting were compulsory?’ Their answer to this may be statistically downweighted, but it will still be added to the total for one party or another, rather than being listed under ‘Don’t know’.

This seems a very bad practice. If a research company were presenting consumer reaction to a new shampoo, I would expect to see a percentage figure for the undecided. Not listing such people separately creates a false impression of certainty. You can apply all the statistical models you like, but the voting behaviour of swing or undecided voters is best predicted by the situation, rather than by anything such people say. If, for instance, you have an incumbent government generally perceived to be doing a tolerable job, and are faced with a high-risk alternative — as in 1992, 2001 or 2015 — the undecided will lean heavily towards the status quo. Had the DKs been listed as a separate figure, more people would have expected Tory success this year.

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Shy Tories are only part of the story. Some DKs would never vote Tory or Labour, but will stay at home if not impressed by any alternative. Finally there may be a ‘Francis Bacon’ effect — where people default to the Conservatives as a least-worst option (the artist explained that he voted Conservative not because he believed they were about to build the New Jerusalem, but because they ‘seem to make the best of a bad job’).