Embed Size (px)
Citation preview
www.NCPolitics.UK
Predicting Polling Failure
Matt SinghNumber Cruncher Politics
@MattSingh_ | @NCPoliticsUK
www.NCPolitics.UK
Bio – Matt Singh• Background in Finance and economics• Started Number Cruncher Politics Sep 2014• Aim is to spread the understanding of polling
and elections to a wider audience
@MattSingh_ | @NCPoliticsUK 2
www.NCPolitics.UK
1992 revisted• The reason for my instinctive skepticism• Polls pointed to a narrow Labour lead, but
result was a Conservative overall majority• Net error of 9 points
@MattSingh_ | @NCPoliticsUK 3
www.NCPolitics.UK@MattSingh_ | @NCPoliticsUK 4
www.NCPolitics.UK@MattSingh_ | @NCPoliticsUK 5
www.NCPolitics.UK
2015 polls and results
@MattSingh_ | @NCPoliticsUK 6
www.NCPolitics.UK@MattSingh_ | @NCPoliticsUK 7
www.NCPolitics.UK
The spiral of silence• Observation: In phone polling, don’t knows
break for the party they voted for previously• In 1992, majority of supposedly undecided
voters had voted Conservative in 1987• This year, some polls found a similar pattern
@MattSingh_ | @NCPoliticsUK 8
www.NCPolitics.UK
Divergence from fundamentals• “I can find no example of a party losing an
election when it is ahead on both leadership and economic competence”
– Peter Kellner, YouGov President, April 2014
@MattSingh_ | @NCPoliticsUK 9
www.NCPolitics.UK 10@MattSingh_ | @NCPoliticsUK
www.NCPolitics.UK 11@MattSingh_ | @NCPoliticsUK
www.NCPolitics.UK 12@MattSingh_ | @NCPoliticsUK
www.NCPolitics.UK@MattSingh_ | @NCPoliticsUK 13
www.NCPolitics.UK@MattSingh_ | @NCPoliticsUK 14
www.NCPolitics.UK
Current thinking – what it’s not• Late swing• Herding• Sabotage
@MattSingh_ | @NCPoliticsUK 15
www.NCPolitics.UK
Current thinking – turnout?• Likelihood to vote questions implied a turnout
of over 90% in some cases• Actual turnout was 66%• No shows may have been unrepresentative• Evidence of people lying about having voted
@MattSingh_ | @NCPoliticsUK 16
www.NCPolitics.UK
Current thinking – wrong answers?• Evidence of people lying about having voted• Might they also lie about how they voted?• Some inconsistencies in answers
@MattSingh_ | @NCPoliticsUK 17
www.NCPolitics.UK
Current thinking – sample imbalance?• Some unexplained patterns in microdata…
@MattSingh_ | @NCPoliticsUK 18
www.NCPolitics.UK
Using polling – house effects• Systematic difference between pollsters’
results owing to methodological differences• Can be interpreted as the difference two
pollsters would get in identical conditions
@MattSingh_ | @NCPoliticsUK 19
www.NCPolitics.UK
Using polling – don’t know, do care• Some people answer, but many don’t• Don’t knows can vary substantially between
pollsters• Don’t knows can be heavily biased
@MattSingh_ | @NCPoliticsUK 20
www.NCPolitics.UK
Using polling – past voting behaviour• Gives a breakdown of what different parties’
voters think• Allows a cross check on sample reliability• Can be used for weighting
@MattSingh_ | @NCPoliticsUK 21
