Stephen Fisher from Oxford University has written an excellent blog this morning using British Election Study data, in which he outlines what it suggests about constituency variation in party performance. You can read it here.

In it, he discusses the declining vote share of the Liberal Democrats, stating that they ‘are clearly losing most in the seats where they started strongest and losing least where they started weakest’. As he rightly outlines, this is, in part, inevitable. The Liberal Democrats’ current polling share is down about 15 or 16 points compared with where it was in May 2010. In over 100 seats, the Lib Dems got less than 16% of the vote, meaning that they have to lose a greater percentage of vote share in other seats.

This leads Fisher to the following conclusion:

The implications for Liberal Democrat seats are straightforward. If they are indeed losing most heavily in the seats they are defending they are set to lose several more seats than national polls with uniform swing would predict.

A few thoughts in response to it.

1. The data in the BES suggests, as have other polling companies, that Labour are set to be the biggest beneficiaries. They can only have so much of an impact on Lib Dem seats, given that it is the Conservatives who are in second place in 37 of the Lib Dems’ incumbent seats.
2. Following on from above, there are a great many seats where the Lib Dems came second with a large share of the vote. In many of these seats, Lib Dem support in local elections has completely dropped off, whilst it has remained somewhat stronger in areas where they have MPs. It is perfectly possible that Lib Dems will lose a great share of the vote in 150-250 seats, but manage to hold on in a number of seats where they have MPs already.
3. Fisher rightly recognises the importance of incumbency and local variation for the Lib Dems, but it is worth stating again. People’s responses, as outlined in polling by Michael Ashcroft, are much more positive for the Lib Dems when asked about constituency voting intention rather than national voting intention.
4. Local variation might well damage the Conservatives too. In many of the seats that the Conservatives might hope to take from the Lib Dems, they might find UKIP splitting their vote enough that the Lib Dems can cling on. Again, polling by Ashcroft would suggest this is currently the case.

Fisher’s analysis is excellent, and will make uncomfortable reading for Lib Dem supporters. However, the points that have been made time and time again by various commentators about local variation remain, and the Lib Dems’ ability to make the most of it in 2015 will determine how many seats they have.