A guest slot from Wulfrun Phil on latest Opinium poll
Published responses to supplementary polling questions are not routinely filtered to limit responses only to those likely to vote in a General Election. That can distort interpretations of “Best PM” polling, because only the responses from those who will vote are ultimately relevant.
Helpfully, Opinium provide so much rich detail in their data tables here that we can apply the filtering ourselves. In their latest poll, the full unfiltered sample of 2002 respondents puts Johnson ahead of Starmer by 35% to 34% in response to the “which would be the best prime minister” question. (Table 7). That though includes responses from those ineligible or unregistered to vote, as well as those who Opinium considers unlikely to vote. By contrast, Opinium’s headline voting intention strips all of these out, being based only on responses from 1209 who will “definitely vote” (Table 2) which reduces to 1087 without “don’t knows”.
Taking just the sample of 1209 definite voters (Table 2), Keir Starmer turns out to lead Johnson as best PM by 40.5% (490) to 36.6% (443), a lead of 4%. Amongst the 1087 who chose a party (VIHeadline table), Starmer’s lead is also 4%, despite the Conservatives’ small 3% lead in voting intention with the same sample.
Starmer’s 4% lead is all the more remarkable because the “Best PM” question is the one generally accepted as giving the advantage to the sitting prime minister. The incumbent by definition is a known quantity surrounded by the trappings of office, compared to a challenger who can only be imagined in the role. Back on 26th March, the last time that Opinium asked the same question with Corbyn as opposition leader, Johnson led Corbyn as best PM by 40%.
Now some might question the extent of Opinium’s stringent filtering. They certainly go further than other companies in asking quite leading questions to weed out those ineligible or unregistered to vote, and also limit VI responses to those who say they will “definitely vote”. On the other hand, their definite voters are still 74% of their eligible voting sample, a proportion above historic general election turnout levels. And given Opinium’s unparalleled achievement in getting each of the Conservative, Labour and LD voting shares spot on in the December 2019 general election, they’ve earned the right to have their methods accepted without reservation.