I did a poll through twitter before the referendum in May 2011.
In it, 72% of the 61 respondants said they would vote 'yes' to av. In the actual referendum only 39% actually responded with a yes vote.
Why the massive discrepency? I asked an almost identical question to the actual referendum, and was very careful to not push my own opinions in tweets I sent out when trying to get responses. If sent a tweet out with a link, I tagged it with either both #tags - #yes2av and #no2av, or with neither tag.
A very similar thing happenned in the 1930's in the USA, on a much larger scale, during a presidential election.
You only need to know that there are two main parties - the Democrats and the Republicans.
A polling company did a MASSIVE phone vote as part of the pre election process. All of these polls showed an overwhelming majority for the Republicans.
When the actual election came around, it turned out to be a Democrat landslide. Why?
A bit of history into 1930's America may help you to find the answer, and then you can try to work out how that relates to my own little poll above.
Answers, comments and ideas are, of course, always welcome.
