This isn't strictly true though, there are any number of polling methods that pollsters use these days including online polling and essentially pre-approved call databases. One of the examples in this article was an in-person poll with 70% response rate.
It's probably more accurate to say it's harder to effectively weigh or average responses in a setting where there are 4 or 5 different channels you are collecting responses from.
That’s interesting, considering I would be far more likely to dodge an in-person poll than any other type. If I see anyone with a clipboard asking people if they’re registered voters, I give a wide berth.
Public radio once had a guest describing their online polling methodology - it was running "Win a Prize" type banner ads. So probably not very representative either.
It's probably more accurate to say it's harder to effectively weigh or average responses in a setting where there are 4 or 5 different channels you are collecting responses from.