Monday, 6 May 2013

The Local Elections in Graphs

After recovering from the all night election analysis at the BBC, I've put together some graphs that show some of the key results in the key wards we cover.

Some topline results

The following graphs show some of the interesting results we saw across the key wards. The first thing to realize about these elections is that they were in very Conservative leaning areas. Even after the UKIP surge, the mean ward result in our dataset looked like this:

Nonetheless, the UKIP share is an incredible performance for a small party. But the picture is very different when we look at the ward distribution. The ward results look surprisingly similar to the status quo with the tories capturing more than half the wards. 

In particular, UKIP goes from second in vote share to fourth in seats. As Steve Fisher, another BBC psephologist and lecturer at Trinity College Oxford, argues, this discrepancy is largely the result of UKIP's vote distribution. The violin plot below shows the vote distribution for each party i.e. how many wards each party got a given percentage of the vote in. If we look at the Liberal Democrats and Labour, they show a highly skewed distribution: they get very low shares in a high proportion of wards with a long tail of better performances where they manage to get seats. By contrast, the UKIP vote is close to normally distributed with little skew. 

The point is inadvertently put best by the UKIP Mayor of Ramsey who tweeted:
The distribution of UKIP's vote ensures that they receive a very high number of second place results.

It's not only the vote distributions that cause problems for UKIP. It's also the distribution of their vote changes. The following graph shows the distribution of the vote changes for each party since the 2009 elections. Given that the three major parties each started from a more efficient baseline (in terms of votes to seats) than UKIP, UKIP would ideally want to have a more skewed set of changes. However, we see exactly the opposite. Labour made 209 gains from a 7.9 percentage point increase compared with UKIP gaining 118 seats from an 11 percentage point gain. This is at least partially because of it's skewed vote increases. Labour has a long tail of increases which, along with its initially skewed performance, led to its strong ward performance.

Thanks to Steve Fisher, John Curtice and Rob Ford for their work on the results and the whole BBC elections team. Note: this post does not reflect the views of the BBC.

How the BBC elections work

Some background. The BBC monitors the results in a set of councils intended to be representative of the election as a whole. In this election they monitored 21 of the 35 councils. With people posted in each area to phone in the results as they happened. This allowed us (the psephologists) to get an up to the minute picture of the election as it happened (mostly at 2am when there was no election programme on air). We collect a variety of demographic and political information about all of the key wards covered and we use this to help inform the viewers about what the results mean, particularly through John Curtice's analysis.


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