900 people
Yes, only a few people could change the result of the election. After the election you can see where they are. Before the election? Much much harder.
Most of the effort in canvassing isn't about persuading. People are incredibly difficult to persuade. In all my years of canvassing I can't honestly say I got anyone to change their mind. As you indicated it's about differential turnout. Find out who your supporters are and get the buggers to vote. That is why people sit on polling stations, and collect the data.
If you're worried about the influence of Facebook or big data on that then there is an incredibly easy solution. Make voting compulsory.
Biting the hand that feeds IT
