What is Margin of Error Polling?

Chris Hanretty is a Professor of Politics at Royal Holloway, University of London. His research spans empirical legal studies and studies of public opinion and voting behaviour. He is the winner of the UK Political Studies Association’s Richard Rose Prize (for a “distinctive contribution to the study of British politics”) and the 2018 Philip Leverhulme Prize.

The Professor introduces three important new concepts/ideas:

1. The first is “margin of error” which you may have heard of but which is a tricky concept to actually understand well. For now, let’s just say that where there is a survey estimate there is also uncertainty about the estimate and the margin-of-error concept represents an attempt to quantify some of this uncertainty.
2. The second is that the answers that people give to a survey might be wrong. Specifically, Chris raises the possibility that people might say that they are going to show up and vote but then not actually do so in practice. This is not an entirely new idea for us, falling under the broad category of “how is that measured?” Still, it’s new enough that it’s worth highlighting.
3. The third is that national vote shares may have only a loose connection with election results. The best recent example of this truth is the Trump-Clinton election. We can say that the late polls came out fairly close to national vote shares. But a reasonable critic may say that this doesn’t really matter because US presidential elections are not decided by national vote shares.

Discussion

As of now, how do you understand the concept of margin of error? Please don’t do any research. Just go based on the state of your thinking at the moment.