Member-only story
The sub-sample problem
A dearth of Scottish polls leads to desperation.
On social media, people often share survey research of vote intentions. On occasion, you may read estimates from Scotland that are not as they appear.
For example, the ‘UK Briefing’ account posted:
(Scotland) Westminster Voting Intention:
SNP: 37% (-11)
LAB: 25% (+5)
CON: 22% (+1)
LDEM: 10% (+6)
GREEN: 2% (-3)
Via [Redfield & Wilton Strategies], 22 Feb
Changes w/ 15 Feb.
Over 500 users shared this post, which shows a large change in intentions.
This is only a sub-sample. The Redfield & Wilton Strategies poll was of 2,000 GB adults on 22nd February. The survey was of online responses, who were eligible voters in Great Britain. Researchers weighted estimates by age, gender, education, region, and 2019 vote. Vote intention shares also had turnout intention weighting.
One ‘region’ was Scotland: with 154 respondents. In the weighted sample, their responses counted for 180 adults.
There is large uncertainty around these estimates. Assuming a simple random sample, the SNP estimate has a margin of sampling error of seven points. That means an approximate confidence interval surrounding the 37% figure is from 30% to 44%.
