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New working paper from Stuart Perrett, @drjennings.bsky.social , @jonmellon.bsky.social , @cbwlezien.bsky.social and me: Do polls underestimate support for right-wing parties? Assessing variation in polling error by party family osf.io/preprints/so...

Can you say whether this is bias in favour of the left or bias against the right/others? I mentioned this to Stuart at EPSS, but, given that the data are compositional and must sum to 100%, either could be true but the implications are different!

I don't think we can say - we're agnostic to the cause of the errors in the paper because I don't think we can test it from polling data alone, and I think you need a causal story to say whether its driven by one side or the other, with the other bit driven by compositional processes.

Makes sense. Another thought I had was whether you could use log ratios to get rid of the compositional element in the data and see what happens.

Breaking it down further by party family, we see a fairly consistent pattern across the left party families but more variation on the right, with polls tending to underestimate Agrarian and Conservative parties, but not Christian Democratic and Far Right parties.

Obviously, 'on average' doesn't mean polls are always-and-everywhere biased to the left - there is a lot of heterogeneity between elections - but elections are much more likely to have a leftward polling bias than a rightward one.

Lots more analysis in the paper, breaking it down over time and by country, so take a look! osf.io/preprints/so...