The British Polling Council welcomes the publication today of the report of the Independent Inquiry into the performance of the polls in the May 2015 general election. It is deeply grateful to the Chair, Prof. Patrick Sturgis, and his colleagues for their forensic and thorough analysis of why the polls underestimated Conservative and overestimated Labour performance at that election.

The principal objective of the Council is to promote transparency in the reporting of opinion polls, and its members are required to adhere to a set of rules designed to achieve that objective. The Inquiry’s report makes a series of recommendations for changes to those rules.

The Council has resolved that so far as some of those recommendations are concerned, the necessary changes to its rules should be made with immediate effect. Other of the Inquiry’s recommendations require preparatory work be undertaken before they can be implemented, and the Council has agreed that that work should be put in train in the expectation that the consequent rule changes can be introduced early in 2017.

Specifically, the Council has agreed to implement immediately rule changes that will (i) require greater transparency about how polls have been weighted, (ii) specify what changes, if any, have been made since a company’s previous published poll in how the data have been weighted or otherwise adjusted, and (iii) place an obligation on members to supply to any inquiry or committee that has been established by the BPC the micro data set for any poll in which that inquiry or committee has an interest.

Meanwhile, the Council has agreed that work should be undertaken to develop (i) an industry-wide method for calculating the confidence limits associated with a poll’s estimate of a party’s share of the vote, and (ii) an industry-wide approach to calculating the statistical significance of the change in a party’s estimated vote share since a company’s previously published poll. Rules that will require members to publish these calculations for any poll of vote intentions will be introduced once this work is completed. At the same time the Council will also consider how best to respond to the Inquiry’s recommendation that members should register with the BPC the fact that they are undertaking a poll.

The Inquiry also makes a series of recommendations for changing the way in which polls are conducted. It will be for individual member companies to decide how best to take these forward. At the same time, however, the Council is aware of the need to show that due note has been taken of those recommendations and to make clear what changes have as a result been made to the way in which polls are conducted. The Council has thus also resolved that (assuming the next election is held in May 2020) it will issue a report in the second half of 2019 that describes the methodology that is being used its members in the run up to the next election and how this methodology has changed since 2015.

Prof. John Curtice, President of the British Polling Council, said, ‘The Inquiry has undertaken what was an important but demanding task in a timely and professional fashion. I am confident that all those with an interest in understanding the difficulties that beset the polls in 2015 will find its report an illuminating and profitable read. The Council now wishes to ensure that its work is put to best use so that the transparency and accuracy of opinion polls is enhanced in future.’