So let me get this straight. We are supposed to believe experts when the predict dire consequences but not when they predict things are not going to be that bad? Or is it when we agree with the prediction then we believe in them? Or are there not really any experts at predicting the economic future and Brexiters were right not to be moved by speculation?
I get so confused.
economists massively overestimate the knowledge they actually have when they talk about macro. It has a lot to do with the way economics is taught and practised nowadays. That is not just a problem of economics, but of social science in general. These academics/experts come up with a lot of genuine inside, but also with a lot of bullshit. The mechanisms of self-correction, that is incredible successful in natural sciences doesn't work anywhere near as good in social science. That is mostly down to the complexity of the subject and they way knowledge is actually created/checked in these fields. There are also cultural problems (a lot of delusion) and issues of bad incentives. So the answer would be to trust some experts, but not all. Obviously all these things apply to the brexit and the remain camp.
That doesn't mean, that we can't make any prediction at all about future developments. There are a lot of good reasons to believe that Brexit will hurt the British economy. Yet when somebody is pretending to put an exact number to these things based on models that use 10th grade maths, I'd be rather sceptic.
Lets take a look at the business insider article about the UBS memo: When somebody is coming up with numbers like this they are usually full of shit. Economic predictions are always about probabilities. So presenting this number without any confidence interval or at least a basic discussion about different out-comes and their probability means that this prediction has no credibility.
If we look at the content of their argument it boils down to "we don't think that a hard-brexit is likely, while markets are overestimating the likelihood of such an event". Predicting the outcomes of this negotiation-process is just random guess-work. It is also worth noting, that they don't dispute that the pound could fall further if it comes to a "hard-Brexit".
So you could re-phrase their argument like this: If the outcome of the negotiations doesn't change a lot for the economy, the pound might rebound to the value that it had before the vote. Well...I don't disagree with that.