Are there some other measurements based on something else, or is it something we now can never know as a result of mail in ballots having no polling and an expected different statistical distribution?
I suggest looking at states like Oregon, Washington, Colorado, Utah, etc. that only do mail in voting and see how they measure what used to be measured by exit polls.
> Are there some other measurements based on something else
For 2016 and 2018, Pew had validated voter datasets, based on people in their American Trends Panel who were matched against voter databases and thus known to have voted. Assuming they do the same thing (or some other reputable firm does something similar, or ideally both) for 2020, that would probably be the best data source.
Are there some other measurements based on something else, or is it something we now can never know as a result of mail in ballots having no polling and an expected different statistical distribution?