This by Fraser Nelson in the Spectator (HT Tim Harford) starts well: “Sometimes, George Osborne’s dishonesty is simply breathtaking.” Who could disagree with that? Except that the statement Nelson objects to is the following:
“Britain would be permanently poorer if we left the European Union, to the tune of £4,300 for every household in the county. That’s a fact everyone should think about as they consider how to vote.”
Nelson does not object to the economics behind the number, set out clearly in a Treasury study released yesterday. (For an excellent review of the study, which makes both of the points I make below, see Chris Giles here.) Instead he has two objections:
With economic growth we would not be poorer under Brexit, just less richer than we would have been if we had remained in the EU
The household figure is derived by dividing the GDP ‘loss’ by the number of households in the UK.
Nelson makes the point that household after tax income is only about two thirds of GDP/households. So implicitly he is saying is that we shouldn’t count lower taxes (and therefore government spending) and investment (future incomes) when assessing whether people would be poorer. But that seems silly. We all benefit from total government spending and investment, so we would feel less well off if we lost some of that. 
Indeed I have done exactly as the Chancellor has done when assessing the impact of 2010 austerity. I calculated, using OBR figures, that austerity cost each UK household at least £4000. The two figures appear comparable, but in fact they are not. My figure is a total one-off cost, on the (admitted very optimistic) assumption that the UK economy had completely recovered from 2010 austerity by 2013. The Brexit cost is a continuing loss each year.
Alas for Fraser Nelson dividing any GDP loss by the number of households is standard practice among economists (see John Van Reenen here for example), and we do it to make our analysis more relevant to those who do not commonly think in terms of GDP. It is also common practice to think about counterfactuals: if we did X (Leave) rather than Y (Remain) how much better/worse off would we be. It is just much clearer to do things that way. Who knows how much richer we will be by 2030: that would be a pretty unreliable forecast, because it depends on pretty well everything. In contrast we can be much surer (although still uncertain) about what the impact of just one change (leaving the EU) will have.
Now if you wanted to avoid any ambiguity, you could rewrite the first sentence of the Chancellor’s statement as follows:
““Britain would be worse off if we left the European Union compared to if we stayed in, to the tune of £4,300 for every household in the county by 2030, and for each and every year after that.”
If this is honest, does that make the original version dishonest. I do not think so.
If this report illustrates anything, it is that it would have been much more effective to have launched a 2003 joining the Euro type exercise immediately after the 2015 election victory, consulting widely among outside experts, and perhaps getting some of them to write key parts of the report. That would have produced a wider range of numbers for the cost, and the Chancellor could have then chosen the higher one, simply inserting ‘up to’ in front of it. But here I am, defending George Osborne and advising him on spin. I think I better go and lie down for a while.
 Slightly pedantic economic point: we should really use GNP rather than GDP, but it makes little difference here.