THE impact of leaving the European Union on Britain’s economy may be the most heated issue of all as the referendum on June 23rd approaches. Many of those who are unsure how to vote say they will decide on the basis of whether Brexit is likely to make them better or worse off. The arguments are hard to assess. Andrew Tyrie, the Tory MP who chairs the Commons Treasury select committee, which is inquiring into the costs and benefits of EU membership, says both sides in the debate “are prepared to set aside all qualifications and restraints in the wilder claims they make.” He hopes his committee can do better, though it too is bitterly divided.

Mr Tyrie notes that, when it comes to Brexit, “the central problem is that there is no counterfactual.” In October, for instance, a Bank of England study concluded that EU membership had boosted the British economy by making it more dynamic. That is hard to square with Brexiteers’ claim that membership has been damaging. Yet the cause of the new dynamism could be something unrelated: perhaps, as Eurosceptics say, the Thatcherite reforms of the 1980s, lower taxes or less red tape.

The missing counterfactual is even more problematic in assessing the economic effects of Brexit. Nobody can be sure what access Britain will have to the single market, what its regulatory regime and migration rules will be, or how long any of these may take to negotiate. Several teams of economists have had a go at guessing. The table shows the conclusions of six of the most comprehensive studies. The wide range of GDP predictions demonstrates how uncertain the outcome is.

One thing both pro- and anti-EU voices can agree on is that the short-term impact of Brexit is likely to be negative. Uncertainty over future trade arrangements has already reduced confidence in sterling and investment could well be discouraged. The Bank of England calls Brexit the biggest risk to domestic financial stability. That Britain is running a record current-account deficit, which has to be financed by capital inflows, makes it all the more vulnerable.

The longer-term effects are more controversial, although most economists reckon that they too are likely to be negative. That is not least because it can take many years for an economy to recover forgone short-term output (if it does). Broadly speaking, economists find five ways in which Brexit could affect future GDP. Losses arising from lower trade are by far the biggest. Later this month the Centre for European Reform, a think-tank, will publish a revised version of its 2014 study on Brexit, based on the work of economists from Groningen University in the Netherlands. It concludes that Britain’s trade with the EU has been 55% greater than it would have been without membership—and that there have been no detectable losses from trade diverted from third countries towards the EU. Even if only some of these gains were at risk from Brexit, they would hugely outweigh the second effect, the economic benefit from cutting Britain’s annual net contribution to the EU budget of some £8.5 billion ($12 billion). The budget gain is also swamped by likely losses from the third factor, lower foreign investment. Brexiteers argue that this will be unaffected, but the evidence is that a large chunk of foreign investment, especially in financial services and cars, has come because of Britain’s EU membership. Gains from a fourth possible factor, fewer onerous rules, are largely illusory. Analysis by the OECD, a rich-country club, finds that British labour and product markets are already among the least regulated of all its members. The fifth consideration is migration. Were Britain to impose tighter controls on EU migrants post-Brexit, growth would depend on attracting from elsewhere the skills its economy needs. Yet it is politically unrealistic to believe that Britons who have just voted to leave the EU partly to curb uncontrolled migration from eastern Europe will want to welcome many more migrants from places like India and Africa.

The Treasury is due to produce its own assessment of EU membership later this month. It is likely to conclude that the economic effects of Brexit would be negative, and that the short-term risks to Britain’s economy are substantial. Economics is accordingly the Remain campaign’s strongest card—provided the campaigners manage to play it well.