A report into why pollsters in the UK got the result of last May's general election so wrong has found that the fault lay largely in the samples used by polling companies.
Most polls had put the Conservatives and the Labour Party on a dead heat, predicting a hung parliament and opening-up talk of potential coalition partners.
The actual result gave the Conservatives an overall majority.
The investigation was commissioned by the association of pollsters and was carried out by a panel of statistical experts.
They found that the polls contained too many younger voters and too few elderly ones.
Younger voters are seen as more likely to vote Labour with older voters more likely to vote Conservative, and more likely to cast a ballot on election day.
The panel also discussed the possibility of "herding", which is where pollsters considering ways to adjust their raw data select the option that produces the most "reasonable" results, or those results which they perceive to be those in line with other polls.
However, the panel said if "herding" did occur it was unintentional.
The accuracy and impact of opinion polls remain very salient issues ahead of a referendum on whether Britain should remain in the European Union.
Polls suggest a tight race between the "in" and "out" campaigns.