Turnout is the great unknown in elections and can dramatically skew results.
Over the last few years we have tended to focus on the big trends in turnout. Turnout used to be regularly above 80% but in recent years only around 6 out of every 10 people registered to vote has turned out. This has led many people to diagnose a crisis in democracy and question the legitimacy of party politics and Westminster democracy.
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On the basis of the admittedly few current results turnout is standing at 60.4% so is in line with recent years.
Yet, often the more interesting story happens beneath the headline figures. There can be spikes in turnout in specific places leading to unpredictable results, or we can see the vote of one party explode or collapse.
So, what might we expect to see as the results come in?
In some seats turnout may plummet as party voters decide not to switch their votes. This may happen in traditionally Liberal Democrat seats as voters decide to disengage from Westminster politics after seeing what a Government including Lib Dems looks like in practice.
Elsewhere turnout may soar where it has traditionally been low due to the success of insurgent parties. Rotherham, for example, where turnout in 2010 was 59% or Doncaster Central where it was 55.5% may see an increase. These are areas where UKIP are expected to do well and it could be the party tempts many voters who have previously stayed at home to make the walk to the polling station.
All these unknowns make it hard to judge what will happen with the national result. What we can say is that it will be interesting in the coming days and weeks to look not just at national turnout trends but also at turnout in individual constituencies across the country.
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