What the polls really mean for the future of Scotland
- 15:08 09 September 2014 by Jacob Aron
Is Scotland about to leave the UK?
Two opinion polls published this week show that the “yes” campaign has
breached the 50 per cent barrier and could be on track to win the Scottish
independence referendum, due to be held next Thursday. But headlines apart,
polling stats suggest either side could come out on top.
Opinion polls are typically based on a random sample of 1000 people, which
means that even if everything is perfectly random, statistical theories say the
margin for error is 3 per cent. In other words, a 50-50 split could actually emerge
And most polls, while close to random samples, don’t meet the strict
mathematical definition as there may be biases in the people polled – meaning the
error bar could be even higher
“If someone asks us for a margin of error we’ll say 3 per cent, but it is more of a
rule of thumb than anything that’s got scientific validity behind it,” says Anthony
Wells of polling firm YouGov, which published the first yes-leading poll on
Saturday with a 51-49 split.
The margin of error isn’t even the biggest cause of uncertainty, adds Wells. While
statistical models for general election polls in the UK are well established, with
years of historical data to draw on and tweak the samples, the same isn’t true for
this referendum. “It’s our first time polling a referendum on Scottish
independence so we haven’t done it before and we haven’t learned those
lessons,” says Wells.
Undecided voters are also an important factor missing from the headlines.
YouGov’s poll actually shows “yes” on 47 per cent, “no” on 45 per cent and “don’t
know” on 8 per cent. A TNS poll published today shows a 50-50 split with “don’t
knows” excluded, but the firm places them at 23 per cent. These undecided voters
don’t usually make it into the headlines but will play a crucial role in determining
the outcome. International precedent suggests undecided voters in a referendum
swing towards the status quo, but things may be different when it comes to
Further surveys conducted before the referendum could show whether the boost
in confidence for the “yes” side will translate into more support, but it looks as if
the final vote on 18 September will be balanced on a knife-edge. “We don’t know
who’s ahead, but we can be confident in saying things have got a lot narrower,”
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