Welcome to the University of Birmingham's Poll of Polls for Britain's European Union referendum. From now until the vote on 23 June, we will be assessing all the major surveys of public opinion to assess what can and cannot be said with confidence about the state of the campaign.
THE UNDECIDED HOLD THE BALANCE
After a wobble in the polls last week, the Leave campaign has stabilized in this week's surveys, closing the gap on Remain.
The Financial Times, which includes undecided votes in its overall count, gives Remain a 46-43 edge with 12% still to make up their minds. The Daily Telegraph's overview, which excludes the undecided, has Remain ahead 53-47.
Last week, the Leave campaign appeared to be in trouble, with an ORB poll gives Remain its largest lead since mid-December at 55-42 among those who "definitely" will vote next month. Among all respondents, the margin was even greater at 58-38.
Beyond the headline figure, the specific groups in the survey gave Leave cause for concern, with a weakening of their support among Conservatives, men, and those over 65. Among the over-65s, a majority of 52-44 favoured remaining in the EU, versus Leave's commanding lead in March of 62-34. Men supported Remain by 55-42, almost a mirror image of March when 55% wanted to quit the EU.
However, ORB's latest survey of 800 people, which was published on Tuesday, showed Remain's lead narrowing to 51-46.
The bounce for Leave appeared to be connected to the issue of immigration taking priority over economic concerns, which have been a priority for those supporting Remain. The ORB founded that 52% of voters thought an exit from the EU would improve Britain's immigration system, with only 23% believing that continued EU membership was the answer.
Even better news for Brexit came from Tuesday's ICM poll in The Guardian, with Leave taking the lead over Remain in both phone and on-line surveys. In the phone poll of more than 1,000 people, Leave had a 45-42 lead with 13% undecided. The on-line result from more than 2,000 respondents was similar: 47-44 for Leave, with 9% undecided.
WHAT DOES IT MEAN?
The obvious answer is that the outcome on June 23 is in the balance, with those yet to decide likely to be instrumental in the result. The uncertainty is bolstered by several features of the polls.
Firstly, there has been a good deal of volatility in surveys. Less than a month ago, a bump for Leave gave it a two-point advantage over Remain. That in turn was a notable shift from mid-April, when Remain had a 10-point lead.
So, although it has not been measured by most polling, there appears to be a significant proportion of "soft" voters in both camps, who could easily switch in the remaining weeks. This assessment is bolstered by a glance at the Don't Knows, who have generally been between 10% and 18%, and as high as 30% in one survey, since mid-April.
Adding to the unpredictable is the sharp difference between polling by phone, which has given Remains lead of 18% in the past two weeks, in contrast to online polling which has forecast the outcome as a virtual dead heat. It remains to be seen if Tuesday's ICM poll, with its convergence of phone and online results, gives some stability.
Secondly, although the ORB poll has made a useful distinction between those "definitely" voting and those who might, it did not indicate how much either camp might be able to turn possible supporters into confirmed votes.
The bottom line remains that turnout will be key on June 23. If one side is more successful than the other in convincing people to make it into the polling booth, that could decide the outcome.
That fundamental is linked to the third point. While last week's ORB poll noted a weakening in the Leave campaign among some groups, it did not pick up on a secure boost for Remain among others that are key. The most important could be voters aged 18 to 25.
The general sentiment among the younger voters in surveys is for Remain, but there is uncertainty as to whether this is committed support. Will they choose the future of the EU over other activities on that Thursday in June?
Professor Scott Lucas
Professor of US Politics and International Relations
Department of Political Science and International Studies