What does a latte tell us about currencies? Very little, actually

Purchasing power parity is not the same as the Big Mac Index.

The Wall Street Journal sees what the Economist is having, and it likes it. The latter's Big Mac Index is famous for demonstrating the variation in prices for the same good around the world. Despite Big Macs being basically identical no matter where you are, the dollar price varies wildly, from $6.81 in Switzerland down to just $1.82 in India. It's so influential that it's widely thought that Argentina is exerting pressure on its branches of McDonalds to keep the price down so as to not provide evidence of the nation's tinkering with reported inflation.

So now the WSJ wants a piece of the action, and has created its Starbucks Latte Index. I mean, it doesn't call it that, but that's what they're thinking:

Click to embiggen.

But like the Economist, the WSJ draws the wrong inferences from the variation. They both have a habit of using the data to illustrate purchasing power parity, the idea that some currencies are under- or over-valued because a comparable basket of goods varies in price. So the WSJ's Ira Iosebashvili writes:

One way to determine how currencies stack up is purchasing-power parity, or PPP, which compares the amount of currency needed to buy the same item in different countries. A grande latte at Starbucks, for example, costs $4.30 in New York, but the equivalent of $9.83 using Norwegian krone in Oslo, and just $3.92 in Turkish lira in Istanbul.

Starbucks Lattes and Big Macs both have another unique feature, though, which renders them less useful for comparing the strength of a currency overall: they are both made up of highly fungible goods, produced in two of the most integrated supply chains in the world. McDonalds, for instance, doesn't need to buy artisanal wheat from an individual farm; it can just trade in "wheat" as a mass-produced, internationally-traded com oddity. The company has even invented a product to sell to take advantage of variations in the cost of pork, the McRib.

In fact, for Starbucks, that's even more true than it is for MacDonalds. While Maccy D's has made a big deal out of its promise to only use British beef in its British burgers, most of the countries Starbucks operates in in don't grow their own coffee. That has to be imported from South America or North Africa, and so a Starbucks in London will almost certainly be paying the same for its coffee as a branch in Oslo, despite the difference in retail price being over $6.

What the Starbucks and Big Mac indices actually show is the price of unskilled labour and retail space. Those are the parts of the companies' businesses which, no matter how hard they try, they can't erase national differences from. Operating in Oslo, land of high taxes, is always going to be expensive, no matter how strong or weak the krone is.

The Starbucks index even makes this clear, thanks to the fact that the WSJ has included three American cities. A latte in New York City costs more than one in Detroit, a difference that self-evidently can't be due to the currency variation.

But the really important news is that London is actually one of the cheapest cities in the world for a Starbucks latte. Still overpriced for what it is, though.

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

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Scotland's vast deficit remains an obstacle to independence

Though the country's financial position has improved, independence would still risk severe austerity. 

For the SNP, the annual Scottish public spending figures bring good and bad news. The good news, such as it is, is that Scotland's deficit fell by £1.3bn in 2016/17. The bad news is that it remains £13.3bn or 8.3 per cent of GDP – three times the UK figure of 2.4 per cent (£46.2bn) and vastly higher than the white paper's worst case scenario of £5.5bn. 

These figures, it's important to note, include Scotland's geographic share of North Sea oil and gas revenue. The "oil bonus" that the SNP once boasted of has withered since the collapse in commodity prices. Though revenue rose from £56m the previous year to £208m, this remains a fraction of the £8bn recorded in 2011/12. Total public sector revenue was £312 per person below the UK average, while expenditure was £1,437 higher. Though the SNP is playing down the figures as "a snapshot", the white paper unambiguously stated: "GERS [Government Expenditure and Revenue Scotland] is the authoritative publication on Scotland’s public finances". 

As before, Nicola Sturgeon has warned of the threat posed by Brexit to the Scottish economy. But the country's black hole means the risks of independence remain immense. As a new state, Scotland would be forced to pay a premium on its debt, resulting in an even greater fiscal gap. Were it to use the pound without permission, with no independent central bank and no lender of last resort, borrowing costs would rise still further. To offset a Greek-style crisis, Scotland would be forced to impose dramatic austerity. 

Sturgeon is undoubtedly right to warn of the risks of Brexit (particularly of the "hard" variety). But for a large number of Scots, this is merely cause to avoid the added turmoil of independence. Though eventual EU membership would benefit Scotland, its UK trade is worth four times as much as that with Europe. 

Of course, for a true nationalist, economics is irrelevant. Independence is a good in itself and sovereignty always trumps prosperity (a point on which Scottish nationalists align with English Brexiteers). But if Scotland is to ever depart the UK, the SNP will need to win over pragmatists, too. In that quest, Scotland's deficit remains a vast obstacle. 

George Eaton is political editor of the New Statesman.