All the polling firms selected their samples using a technique known as quota sampling.
ECONOMIST: Why the polls got it wrong last time
Using old-style quota sampling Gallup's polls had shown a Labour lead of 37 points.
The difference this new method can make was dramatically illustrated in January when Gallup made its switch from quota sampling.
Can these problems with quota sampling be fixed?
ECONOMIST: Why the polls got it wrong last time | The
ICM, have gone much further, partly or wholly switching from quota to random sampling.
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