The Polls and The 2015 ElectionJohn Curtice

9 June 2015

22

Two Halves The exit poll

The pre-polling day polls

33

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!

44

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

55

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 2010.

129 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.

66

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.)

77

How close were we?

Con Lab SNP Lib Dem Others0

50

100

150

200

250

300

350316

239

58

1027

331

232

56

823

Forecast Outcome

88

The Previous Record - 2010

Con Lab Lib Dem Others0

50

100

150

200

250

300

350307

255

5929

307

258

5728

Forecast Result

99

The Previous Record - 2005

Con Lab Lib Dem Others0

50

100

150

200

250

300

350

400

209

356

5328

198

356

6230

Forecast Seats

1010

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

Con Lab UKIP Lib Dem Green Others0

5

10

15

20

25

30

35

40

34 34

13

9

5 6

38

31

13

8

46

Poll Average Result

1111

A Longer Term Pattern?

1992 1997 2001 2005 2010 2015

-6

-4

-2

0

2

4

6

-5

-1

-3

-1-1

-4

43

4

1

-2

3

ConLab

Ave

rage

Err

or in

Pol

ls

1212

Modal Differences

Con Lab UKIP Lib Dem Green Others0

5

10

15

20

25

30

35

4035 34

119

4.56.5

33 33

14

9

5 6

Phone Internet

1313

Possible Explanations Late Swing

Shy Tories

Lazy Labour

Question Order/Wording

Poor samples that are inadequately weighted (perhaps because they cannot be!)

1414

A Shortage of Young Voters

YG (18-39) Populus ICM Ipsos MORI0

5

10

15

20

25

30

35

40

30

2624

22

37

29 30 29

Unweighted Weighted

% 1

8-34

1515

An Excess of Middle Class Ones

YouGov Populus ICM Ipsos MORI0

10

20

30

40

50

60

7061 61 62

5956 54 56 54

Unweighted Weighted

1616

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: www.ncrm.ac.uk/polling/