[Melian]

The Z-score, or standard score, is the number of standard deviations a given data point lies above or below the mean.

For more on the survey:

https://electionstudies.org/data-center/2020-exploratory-testing-survey/

[meyer]

Thanks for the additional info regarding the Z-score and the survey itself. Sometimes, it pays to see what questions were used to determine the result, and that is provided at your link.