The idea that Liberal Democrat and Conservative political fortunes are tied together comes in two forms. The basic – that with both being in government, the public’s overall view of the government (and in particular its economic record) will heavily determine its view of both parties come the next election. Sink or swim together then. Then there is version which adds an asymmetric twist. Namely that if the public views the coalition as a failure both parties will sink together, but if the public rates the coalition as a success, being the smaller of the two parties means the Liberal Democrats won’t necessarily get their share of the credit.
What does the polling data show?
I’ve put together three simple plots, using the data from my opinion poll database. Taking the 700+ national voting intention opinion polls since the general election, I’ve plotted three graphs, showing how the level of Liberal Democrat support (on the y-axis) varies compared to the level of Conservative, Labour or Other support in turn (the x-axis).
Taking the Lib Dem versus Conservative one first, the data shows a weak link between the level of Lib Dem and Conservative support. The two parties are sinking or swimming together somewhat, but with enough variation to push the analogy into breakdown by talking about how the two parties are like neighbouring swimmers, with one able to be on top of a wave just as another is in a trough but both experiencing the same overall sea conditions.
There is a much clearer picture when Liberal Democrat and Labour support is compared:
Finally, here is how Liberal Democrat support varies with that for ‘Others’, showing more similarity with the Labour than the Conservative picture if you work out the trend lines and correlations:
In other words, this poll data – as far as it can answer that question – shows a modest degree of sink or swim together. Lib Dem fortunes are at odds with those of Labour and Other parties but do, to a degree, move up and down with that of their coalition partner. However, there is more than enough variation around the averages to attempt to finesse or buck the underlying trends. Whether politicians manage to do such things by luck or by judgement is another story…