Not sure quite what you mean, but I don't think it's right to think about this as 'forecasting a long way out'. In the jargon, we'd insist that comparing 2 conditional forecasts is much more precise than doing an unconditional forecast. To explain in plain language...
You cannot very easily forecast my weight 10 years from now, even with data on my current lifestyle. Because lots of things can happen. [Just as in the global economy].....
But you can, using medical science, accurately foretell that other things equal, if I give up craft beer and crisps [very implausible if you knew me] I would be lighter than otherwise.
Of course there are a few econs supporting Brexit, against the 100s on the other side. But they are also doing conditional forecast comparisons. The disagreement is about the effects of the policy experiment [raising barriers with Europe, lowering them elsewhere]. Eg on gravity
The unknowns are: will the effect of gravity lessen or worsen? Will the effect of trade on income per head lessen or amplify? How deep could we make our new FTAs despite the objections of the sovereignty crowd? How shallow will the EU one end up being at the end of Brexit?
But those uncertainties are like the clouds around my future lifestyle when you are forecasting my weight. So if I give up crisps and beer, there is still the q of whether a new artisanal chocolate shop opens up nearby etc.
They don't cloud the statement about what would happen to our income per head IF trade barriers were lowered elsewhere and raised with the EU. That is known very well.
A direct analogy is: just because you don't know whether an artisanal chocolate shop is going to open up near me [hence you can't forecast my weight 'a long way out'] doesn't negate that I should in fact give up craft beer and crisps.
I wrote a version of this recently, following insinuations that BoE forecast updates made the Brexit stuff look all fuzzy. longandvariable.wordpress.com/2018/02/08/cha…
If you think about it, economic 'gravity' is everywhere. It's the explanation for why we get together in megacities, cities, towns and villages. And related to why people get together in firms, rather than trading for every piece of work and task as individuals.
Not directly mentioned in this conversation, I'll add remarks about the common practice [usually, but not exclusively it has to be said] on the Leave side of saying 'you see, UK is doing better than those short term forecasts, which just shows the whole Remain worry is rot.'
The basic defence of the consensus [eg BoE] forecast is that Brexit has made life worse. Lower £, higher inflation as a consequence, and lower real wages. Also lower business investment growth.
Also, we have a stronger global economy. And, if you think Brexit voting consumers had taken the view that Brexit wasn't a long term hit [incorrectly of course] why would they cut consumption when they got what they wanted?
The BoE like to play up the effect of their interest rate cut to 0.25pp and the extra QE. But this did much less than they would like us to think; serving to signal that they would try to combat a panic, but not much more than that.
Lurking here is another defence, which sheds light on the activity of forecasting. If you throw a dice, and get a 6, that does not invalidate me warning you that the mean score is 3.5 and there is a sizeable chance you will get only 1.
This point applies as much to those who would defend the gloomy short term post Brexit forecasts as to those who would attack them.
Pulling back from that detail a bit, the short term forecast evaluation anyway does not bear hardly at all on the merits of the gloomy long term asessment of the impact of raising trade barriers with EU, and trying to lower them elsewhere.
Why? Because we have not yet raised trade barriers with the EU, nor lowered them elsewhere. And there is a lot of uncertainty about how much we will do, if any, of either of those things.
The post Brexit UK economy does shed A BIT of doubt on the validity of assuming that people will i) assume we will leave in short order ii) correctly calculate their own income hit iii) correct spending now to compensate.
To reprise - if consumers had been able to correctly get the hit to their future income, many of them - except those entirely voting on cultural or sovereignty grounds - would not have voted to Leave in the first place.
