The report, authored by YouGov’s Anthony Wells and Doug Rivers, focuses on how politically interested people who respond to polls are, and how that impacts on the age of people in samples. “In my view it’s the core issue that caused the problems in May, it’s also the issue that is more likely to have impacted on the whole industry (different pollsters already have different age brackets) and the issue that more challenging to solve (adjusting the top age bracket is easily done),” says Wells.

“People who take part in opinion polls are more interested in politics than the average person. As far as we can tell that applies to online and telephone polls and as response rates have plummeted (the response rate for phone polls is somewhere around 5%) that’s become ever more of an issue. It has not necessarily been regarded as a huge issue though – in polls about the attention people pay to political events we have caveated it, but it has not previously prevented polls being accurate in measuring voting intention.

“The reason it had an impact in May is that the effect, the skew towards the politically interested, had a disproportionate effect on different social groups. Young people in particular are tricky to get to take part in polls, and the young people who have taken part in polls have been the politically interested. This, in turn, has skewed the demographic make up of likely voters in polling samples.”

The report can be accessed here.