Do stats etc for work. I know how very hard it is to perform demographic profiling correctly. It's never going to be right. And easy to be wrong especially with close calls.
You can break down demographics to your hearts content. Race, socio-economic, gender, age,.. Very soon you get massive samples and it becomes expensive.
It gets even harder when you consider certain people never do polls. Telephone or post or Internet?
Then you scale up, have to consider people change their mind over news stories last minute and due to current predictions, etc.
You have to even be careful postcode sorting as even number house numbers may be on an expensive side of the street!
So many factors, so easy to bias in the wrong way!
Messy game