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.

David Cameron addresses pupils at an assembly during a visit to Corby Technical School on September 2, 2015. Photograph: Getty Images.
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Can Cameron maintain his refugee stance as he comes under attack from all sides?

Tory MPs, the Sun, Labour and a growing section of the public are calling on the PM to end his refusal to take "more and more". 

The disparity between the traumatic images of drowned Syrian children and David Cameron's compassionless response ("I don't think there is an answer that can be achieved simply by taking more and more refugees") has triggered a political backlash. A petition calling for greater action (the UK has to date accepted just 216 refugees) has passed the 100,000 threshold required for the government to consider a debate after tens of thousands signed this morning. Scottish Conservative leader Ruth Davidson has tweeted: "This is not an immigration issue, it's a humanitarian one, and the human response must be to help. If we don't, what does that make us?" Tory MPs such as Nicola Blackwood, David Burrowes, Jeremy Lefroy and Johnny Mercer have similarly appealed to Cameron to reverse his stance.

Today's Sun declares that the UK has "a proud record of taking in desperate people and we should not flinch from it now if it is beyond doubt that they have fled for their lives." Meanwhile, the Washington Post has published a derisive piece headlined "Britain takes in so few refugees from Syria they would fit on a subway train". Labour has called on Cameron to convene a meeting of Cobra to discuss the crisis and to request an emergency EU summit. Yvette Cooper, who led the way with a speech on Monday outlining how the UK could accept 10,000 refugees, is organising a meeting of councils, charities and faith groups to discuss Britain's response. Public opinion, which can turn remarkably quickly in response to harrowing images, is likely to have grown more sympathetic to the Syrians' plight. Indeed, a survey in March found that those who supported accepting refugees fleeing persecution outnumbered opponents by 47-24 per cent. 

The political question is whether this cumulative pressure will force Cameron to change his stance. He may not agree to match Cooper's demand of 10,000 (though Germany is poised to accept 800,000) but an increasing number at Westminster believe that he cannot remain impassive. Surely Cameron, who will not stand for election again, will not want this stain on his premiership? The UK's obstinacy is further antagonising Angela Merkel on whom his hopes of a successful EU renegotiation rest. If nothing else, Cameron should remember one of the laws of politics: the earlier a climbdown, the less painful it is. 

George Eaton is political editor of the New Statesman.