Peter Kellner: Why do the polls in Scotland vary so much?

COMMENT: YouGov president Peter Kellner takes an in-depth look at the reasons behind the varying results of opinion polls by the country’s main pollsters.
Kellner’s comments come after a YouGov poll for The Times showed a drop in support for a ‘Yes’ vote in September’s referendum.

YouGov’s latest survey, for The Times, shows that a large majority of Scots intend to reject independence in the referendum on September 18. Among those who take sides, 39% intend voting Yes and 61% No. TNS and Ipsos MORI have recorded similarly decisive verdicts in recent weeks.
However, ICM (45% Yes, 55% No), Survation (47%-53%) and Panelbase (48%-52%) say the race is much closer. What is going on?

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