Political Polls
Why are all the polls different?
Realclearpolitics is a political site that is often cited by news organizations because it aggregates political stories and polls. Of particular interest are the RCP averages that group a large number of polls released over time and provide a single average across all of them. This average indicates the spread between the percentage support for each candidate in each poll. I took a screenshot of their page reporting 2024 General Election results: Trump vs. Biden on June 30th, 2024. This was just after the first presidential debate on June 27th.
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The RCP average is at the top at +1.9, followed by three one day polls in the green box I used to highlight them. Those three polls are the first ones released after the debate performance of the two candidates and are special reaction polls compared to the multi day polls taken previously.
So the big question is: Why do all three polls have a different spread. Two of the polls have Trump ahead and one of the polls has Biden ahead. What's going on here? Why can't any of the polls agree if they're supposed to be measuring the same thing: General Election support of each candidate on June 28th, 2024.
To answer these questions, we have to look for some simple truths about polls. We'll start with that stat in the middle labled MOE.