This is the second in a regular series of posts reporting on the state of the parties as measured by opinion polls. By pooling together all the available polling evidence we can reduce the impact of the random variation each individual survey inevitably produces. Our method is preferable to taking the average of all available polls in a ‘poll of polls’ because it also takes into account the estimated biases of the individual pollsters (“house effects”), the effects of sample size on the likely accuracy of polls, and the effects of the sampling decisions pollsters make, which mean their samples are not truly random (“design effects”). Most of the short term advances and setbacks in party polling fortunes are nothing more than noise; the underlying trends – in which we are interested and best assess the parties’ standings – are relatively stable and little influenced by day-to-day events.
Our most recent update on public support for the parties, taken on May 1 just four days before voters across the UK go to the polls in national and local elections as well as the referendum on AV, suggests a slight weakening of the Labour lead over the Conservatives during May, and a slight upturn in support for the Liberal Democrats over the last month. Our current estimate for the Conservatives stands at 34.5%, around the same level as we identified last month. Support for Labour, at 40.4%, is around a percentage point down on the end of April. The Liberal Democrats have experienced a slight improvement from the lows of last month, with our estimated poll share now putting them at 9.8%, more than a percentage point higher than in April.