The Polls and The 2015 Election John Curtice 9 June 2015

11 Two Halves The exit poll The pre-polling day polls

22 The Difficulties of Exit Polling Very geographically clustered sample. No precinct level counts, so difficult to draw a sample of districts that is known to have been representative of the result last time. Some polling locations are easier to cover than others! Relatively high (and potentially differential) refusal rate. Most voting takes place in the early evening, giving little time to analyse the data!

33 The Solution Geographical variation in change in party support much less than variation in the level of party support. Thus any sample of locations more likely to produce an accurate estimate of change in vote share than in level. But need an estimate of vote share last time. So poll in the same places as last time, and compare exit poll results this time with last time. Invite respondents to complete mock ballot paper

44 The Design in 2015 Covered 141 polling stations. Interview random 1 in n sample, where n function of station electorate. Four were instances where polling district split into two; so 139 estimates of change since were places covered by 2010 exit poll, though some had undergone boundary change. Only two locations replaced. Six new locations added in Scotland and four in areas of UKIP strength. In each case, attempted to select a polling station representative of the constituency.

55 Thereafter… Model the 139 changes (for each party) using whatever constituency data appears theoretically and empirically appropriate. Use resulting equation to estimate change in vote shares in each constituency – and thus vote shares. From these vote shares estimate probability of each party to win each seat. Forecast seats for each party is sum of probabilities. (No national vote forecast.)

66 How close were we?

77 The Previous Record

88 The Previous Record

99 Performance of Final Polls Based on 10 polls whose fieldwork did not end before 5.5; Polls by Opinium; YouGov; Survation; ComRes; Populus; Ashcroft, Ipsos MORI: BMG Research, Panelbase; ICM Research

10 A Longer Term Pattern?

11 Modal Differences

12 Possible Explanations Late Swing Shy Tories Lazy Labour Question Order/Wording Poor samples that are inadequately weighted (perhaps because they cannot be!)

13 A Shortage of Young Voters

14 An Excess of Middle Class Ones

15 The Inquiry Sponsored by BPC and MRS Chaired by Prof. Patrick Sturgis, Director of NCRM Eight other members – 5 academics, 3 commercial researchers None directly involved in polling in 2010 Asked to report by March 2016 First open public meeting, RSS, 19 June Call for evidence: