A couple of days ago, on 1 August, Brad Setser posted that The Economist had picked a good week for a currency cover, and that the Big Mac index agreed with his own work in putting the yuan around 30% undervalued. I replied.

Setser is the Whitney Shepardson senior fellow at the Council on Foreign Relations, and before that he was deputy assistant secretary for international economic analysis at the US Treasury and a senior adviser to the US Trade Representative.
He has spent two decades tracking global capital flows, reserve accumulation, and currency intervention, and his blog Follow the Money is one of the few places where the actual balance of payments data get read properly. I have a great deal of respect for Brad’s work, which is why the disagreement is worth having in public rather than in a footnote.
His number is exactly what the index says. In the July 2026 edition a Chinese Big Mac costs 31% less in dollars than an American one, and in January it was 33% less. The question is what that gap is a fact about.
The proposition is not a throwaway. It says that a persistent gap between a currency’s market rate and its purchasing power parity rate is a fact about the country’s price level rather than a fact about its currency, and if that is right then a good deal of what is written about undervalued currencies is a category error.
Let me be clear about where I start, because the reply reads as though I were reaching for Balassa-Samuelson first. I am not. I start with purchasing power parity, and I start there because it is the decisive factor. Prices and exchange rates move together, and everything else in currency analysis operates on the remainder.
I have forecast exchange rates professionally for a quarter of a century, and PPP has been the starting point of every model I have built. Balassa-Samuelson comes second, as the correction that says the parity a country converges to depends on how productive it is. I have tested that correction many times, in many formats, on many datasets. Never on the Big Mac index.
Which is a strange omission, because the index turned forty this summer.
It first appeared in the print edition of 6 September 1986, in a table of thirteen countries, under the heading of a light-hearted guide to whether currencies were at their correct level. Pam Woodall, then the paper’s economics editor, devised it as a semi-humorous illustration of purchasing power parity, and it gave the language the word burgernomics.
She cannot have expected it to still be running four decades later, in more than fifty countries, twice a year. The anniversary was as good an occasion as I am going to get to run the test again on data I had never used. And with a bit of help from Kaggle, Github and Claude it can now be done relatively fast.
What follows is the result: 2,036 observations, 54 currencies, and thirty years of the index, together with income, productivity, institutions, and governance data for every one of them.
What the index actually measures
Start with the theory, because almost every argument about the Big Mac index is really an argument about purchasing power parity, and most of the people having it have not thought carefully about which version they mean.
Purchasing power parity is one of the oldest propositions in international economics.
Gustav Cassel, who is one of my absolute favourite economists, gave it its name and its modern form during the First World War, when the gold standard was suspended and the practical question was which exchange rates Europe should return to afterwards.
And his answer was that the equilibrium rate is simply the ratio of the two countries’ price levels. So if a basket of goods costs 100 kroner in Denmark and 20 dollars in America, the equilibrium rate is five kroner to the dollar.
The Big Mac index applies exactly this logic to a single good: take the local price of a Big Mac, divide it by the American price, and you have an implied exchange rate that can be compared with the actual one. If the actual rate is weaker than the implied rate, the currency is called undervalued.
Note what this is not. It is not a measure of whether a currency will rise. It is a measure of whether the price level and the exchange rate are consistent with each other. Any adjust might happen through changes in the price level or the exchange rate – or both.
Figure 1 puts every observation on a single chart, with the Big Mac parity rate on the horizontal axis and the actual rate on the vertical, both measured in local currency per dollar and both on a logarithmic scale.
That covers seventy-four currencies over forty years and a span of seven orders of magnitude, from the Swiss franc at one end to the Vietnamese dong at the other.

Figure 1. Parity holds across seven orders of magnitude
The regression slope is 1.0162, which means a forty-year test of Cassel’s proportionality postulate cannot reject a coefficient of one, and the explained variance is 0.982.
Cassel was right!
The bit the chart hides
But now look at the same picture from the other side, because the median absolute deviation from the 45-degree line is 23%.
On a chart spanning seven orders of magnitude that deviation looks like nothing at all, while to anybody actually running money a 23% misalignment is enormous. And that gap is what the rest of this piece is about.
The standard explanation is Balassa-Samuelson, after Béla Balassa and Paul Samuelson, who published it independently in 1964.
The mechanism is straightforward once you separate goods into two kinds. Traded goods such as steel, wheat, and semiconductors have their prices arbitraged internationally, while non-traded goods and services such as haircuts, rent, and waiting a table do not.
Rich countries are rich because they are productive in the traded sector, and that productivity bids up wages across the whole economy, including in the barber shop where no productivity gain has occurred. So the price of non-traded goods rises with income, the overall price level rises with it, and rich countries end up expensive.
A Big Mac is itself mostly non-traded, being beef and bread assembled by local labour in rented premises. Not to mention electricity and taxes.
But Balassa-Samuelson is a statement about productivity, and productivity can be measured in a dozen ways that do not agree with each other.
So I ran the exchange rate equation with each of them in turn, alongside the burger price, a governance term, and a dummy for the four city states (See more on that further below). A negative coefficient means a stronger currency.
| Measure of productivity | n | Curr. | Coef. | t |
| Total factor productivity, PWT | 1,897 | 48 | −27.52 | −2.37 |
| GDP per head at constant PPP prices, IMF | 2,080 | 55 | −20.55 | −4.11 |
| GDP per head at PPP, IMF | 2,036 | 54 | −20.45 | −4.19 |
| Human capital index, PWT | 1,994 | 51 | −16.60 | −0.75 |
| Output per hour worked, PWT | 1,998 | 52 | −16.20 | −3.18 |
| Real GDP per head, PWT | 2,036 | 54 | −14.48 | −3.21 |
| Output per worker, PWT | 2,036 | 54 | −13.63 | −2.66 |
| Life expectancy at birth, UNDP | 1,961 | 53 | −2.38 | −4.71 |
| Human development index, UNDP | 1,961 | 53 | −0.78 | −2.31 |
| Mean years of schooling, UNDP | 1,961 | 53 | −0.15 | −0.10 |
Eight of the ten carry the sign the theory predicts with a t above two – meaning it statistical significant at a 5% level.
Whether productivity is measured at purchasing power parity, at constant prices, per worker, per hour worked, as total factor productivity, or as how long people live, a more productive country has a stronger currency than the burger parity rate implies.
Human capital and years of schooling are the two that fail, and both are stocks of education rather than measures of output, which is not the same thing.
Output per hour is the theoretically correct variable, and in the latest Penn World Table it covers 52 of the 55 currencies, which it did not in earlier versions. Total factor productivity gives the largest coefficient of all, at −27.52, though it is also the least precisely measured.
Life expectancy is the one I keep coming back to. It contains no prices, no exchange rate, and no monetary quantity of any kind, and it still gets a t of −4.71.
Note what is not in the table. GDP per head measured at market exchange rates is the variable most people reach for, and it has no business being here. Convert income to dollars and you have multiplied by the exchange rate, which is the thing on the left-hand side. The relationship that produces looks strong and means nothing.
Figure 2 shows what the surviving relation looks like, with productivity measured as GDP per head at constant purchasing power prices, which is the measure that ends up in the model.

Figure 2. Richer countries have dearer burgers
The slope is 0.23. A country twice as productive as another has a burger price around 16% higher, which is the Balassa-Samuelson effect in its plainest form.
Note the spread around the line, though. At any given level of productivity the burger price varies by 50 log points or more.
Institutions are hard to separate from income
Every empirical exchange rate economist reaches for institutions at this point, and I am no exception.
The trouble is visible in one chart. Figure 3 plots the Fraser Institute’s measure of legal system quality and property rights against productivity. The correlation is 0.75, which leaves 43% of the variation in one that the other does not account for.

Figure 3. Institutions and income move together
I want to be careful about what that does and does not mean.
It is not that institutions are income, and nothing here says that good institutions are produced by being rich. Rich countries have good institutions and well governed countries are rich, and forty years of burger prices will not tell you which way that runs. What the correlation does mean is that the two are very hard to hold apart in estimation.
That shows up as instability. Put several institutional measures in together and they take turns having the wrong sign, because they are all proxies for the same underlying thing and each one absorbs whatever the others leave behind. Which measure survives a general-to-specific search depends on the order in which the others are removed.
So instead of picking one, here is every institutional measure I have, entered one at a time into the same equation.
| Measure | Coefficient | t |
| Fraser judicial independence | −6.82 | −2.67 |
| Fraser legal system | −4.65 | −1.35 |
| Fraser property rights | −3.70 | −1.39 |
| Fraser business regulation | −2.53 | −0.72 |
| WGI control of corruption | −0.46 | −3.05 |
| WGI rule of law | −0.36 | −1.90 |
| WGI regulatory quality | −0.36 | −1.75 |
| WGI voice and accountability | −0.35 | −3.58 |
| WGI government effectiveness | −0.22 | −1.01 |
| WGI political stability | −0.13 | −1.00 |
All ten point the same way. Three are individually significant. The first principal component of all ten, which takes 84% of their common variation, enters at −3.61 with a t of −1.98.
That is the honest version of the institutional result, and it is a better one than picking the survivor of a search. The sign consistency across ten measures from two independent sources is the finding. The magnitude is not: the coefficients span a factor of fifty because the measures are on different scales, and which one is individually significant depends on nothing more interesting than measurement noise.
The equation below uses voice and accountability because it survived a general-to-specific search. I would not defend that choice. Rule of law or control of corruption has at least as good a theoretical claim, and both give a similar answer.
The model
Put it together and the equation is written the way a currency forecaster writes one, with the exchange rate versus the US dollar on the left.
100 × ln(local currency per dollar) = 2.58 + 0.989 × relative burger price − 15.68 × productivity − 0.437 × governance + 27.89 × city state
| Coefficient | t | |
| Constant | 2.58 | 0.45 |
| Relative burger price | 0.989 | 113.22 |
| GDP per head at constant PPP prices | −15.68 | −3.33 |
| Voice and accountability, WGI | −0.437 | −4.60 |
| City state | 27.89 | 2.01 |
n = 2,036, 54 currencies, 1996 to 2025. R-squared 0.9868. Standard errors clustered by currency.
Note what is not on the right-hand side: no exchange rate, in any form, anywhere. The relative burger price is measured in local currency, the productivity term comes from the IMF in constant purchasing power prices, and the governance term is a percentile rank.
A negative coefficient means fewer local units per dollar, which is a stronger currency. So the reading is that productivity and governance both pull a currency above its parity rate, and that the four city states sit around 32% below either.
Every candidate had a sign attached to it before estimation, and anything that came out with the wrong one was removed. Twenty-two candidates went in and four came out. I want the model to be statistically correct and economic theoretically correct.
That procedure is not innocent, and the reported t values are too high because of it.
Selecting on the estimated sign and then quoting the significance of what survives overstates the evidence, and it does so most for the governance term. Read the burger price and productivity coefficients as estimates and the governance coefficient as an indication.
The burger price coefficient is 0.989 with a t against one of −0.99. Again highly significant.
Cassel’s proportionality postulate cannot be rejected, in an equation with no exchange rate on the right, on 2,036 observations across 54 currencies and thirty years.
One more test before the story is told, and it is the one that matters most.
The equation above is estimated in levels across currencies, which means it can be read as a statement about why some countries are dearer than others.
Add currency fixed effects and the question changes to whether the relation holds within a currency over time. It is a harder test, and two of the four terms do not survive it.
| Pooled | Currency effects | Currency and vintage effects | |
| Relative burger price | 0.990 (115.32) | 0.970 (79.37) | 0.968 (81.34) |
| Productivity | −20.55 (−4.11) | −15.59 (−1.72) | −19.34 (−2.15) |
| Governance | −0.345 (−3.58) | **+0.690 (3.16)** | +0.216 (0.86) |
The burger price coefficient barely moves, at 0.97 either way, and productivity survives once vintage effects absorb the common movement in the world price level.
Governance does not survive. It changes sign and becomes significant in the wrong direction. Whatever the governance term is picking up, it is a difference between countries and not something that moves a currency when a country’s own institutions change.
I said above that I would treat it as an indication rather than an estimate. This is why.
That is close to being the whole story. Purchasing power parity, plus The Balassa-Samuelson effect, plus a governance term that is real but hard to size, plus a dummy for four places that are cities rather than countries.
Burgernomics is no evidence of Chinese currency manipulation
Which brings me to the argument that started all of this. Brad Setser as mentioned above that the Big Mac index agrees with his own work in showing the yuan substantially undervalued, and every American administration for twenty-five years has said something similar in considerably stronger terms.
The raw index does appear to show it, since China’s Big Mac has averaged 42% below the American price over the whole period.
However, conditional on the model, I find nothing of the sort.
The yuan has averaged within a few percent of the rate the equation implies, and the sign of the gap flips depending on which productivity measure goes into it: slightly undervalued on GDP per head, slightly overvalued on output per hour, and on the final specification 11% overvalued across the sample with the latest reading essentially on the line. Account for Chinese productivity and there is no unexplained undervaluation left to explain.
Figure 4 puts every currency in the January 2026 edition on one scale, with the United States given a residual of its own rather than assumed to be correctly priced.

Figure 4. Price level and exchange rate misalignment
Meanwhile the two largest unexplained undervaluations in the entire dataset are Taiwan at 21% and Hong Kong at 19%.
The Taiwanese burger is now 61% cheaper than the American one against a model prediction of 21%, and the gap has widened by around 55 percentage points since 1994 while Taiwanese income rose sharply.
The country everybody argues about is the one the model fits best. Just have a look below.
Figure 5 puts the fourteen most traded currencies side by side and shown as they are quoted: units of local currency per dollar.
The dashed line is the rate the model implies, which is the Big Mac parity rate adjusted for productivity, governance, and the city state term. The shaded area on the right-hand axis is the gap between the two, in percent.

Figure 5. The fourteen most traded currencies against the dollar
China is among the tightest fits in the panel. The yuan has averaged 7% away from the rate the equation implies, with the Canadian dollar at 0.5%, the New Zealand dollar at 3.7%, the won at 3.3%, and the yen at 5.5% alongside it.
Taiwan is the failure. The Taiwan dollar goes from roughly fair in the mid-1990s to 47% undervalued today, while the rate the equation implies barely moves. The Hong Kong dollar is the same story without the trend: 55 observations, undervalued in all but one of them, and the city state term takes only part of the gap. It is tempting to say that geopolitics might play a role here – both for Taiwan and Hong Kong.
The Swedish krona has averaged 31% overvalued and the krone 37%, which sounds like a standing feature of both economies. It is not. The krona peaked at 94% in 2011 and reads 9% undervalued in the latest edition.
The Norwegian krone peaked at 116% in 2006 and is now 2% below the line.
The euro has gone from 65% in 2008 to half a percent. All three converged on the model from above, at between one and five percentage points a year, and all three arrived.
Switzerland is the exception that did not arrive. The franc is the standing example of an overvalued currency, and the Swiss Big Mac is the dearest in the world at 9.08 dollars.
It has been converging too, from 106% in 1995 to 22% today, but at 1.7 points a year it is the slowest of the four and it still has two decades to go at that rate. Whatever makes Switzerland expensive is more durable than whatever made Scandinavia expensive. That being said – for all these currencies there are clearly elements of safe haven effects that the model does not fully account for.
The commodity dollars went the other way. Both the Canadian and the Australian dollar were 30% or more above the line during the commodity boom of 2011, and both are now below it, at 9% and 20% respectively. For these two the model reads the cycle rather than a level, and the cycle is the price of iron ore and oil.
How the gap closes
An equilibrium relation is only interesting if deviations from it come back. So the last question is whether they do, and how fast.
The object that has to revert is the real exchange rate: the dollar price of a Big Mac relative to the American one.
I estimated an error correction (EC) equation for it on the annual panel, with the lagged deviation from the model, one lag of the dependent variable, and changes in productivity and governance. 1,154 annual changes across 55 currencies, with years of collapse and hyperinflation removed.
| Adjustment | t | Half-life | |
| Error correction only | 0.0924 | 6.37 | 7.2 years |
| Plus a lagged change | 0.0899 | 5.70 | 7.4 years |
| Plus fundamentals | 0.0842 | 5.36 | 7.9 years |
It reverts, and the estimate is stable. Roughly nine percent of a deviation closes each year, which puts the half-life between seven and eight years, and adding short-run dynamics moves it hardly at all.
The country-level picture is consistent with the pooled one.
The adjustment coefficient has the mean-reverting sign in 40 of the 41 currencies with at least twelve annual changes, though only 16 of those are individually significant, and the median country half-life is three years rather than eight. That gap between the pooled and the median country estimate is the usual one in this literature: the pooled coefficient is dragged towards zero by the currencies that barely move.
Push the deviation further back and it fades in the way it should. Measured from two years earlier the coefficient is 0.078, from three years earlier 0.052, both still significant on the same sample.
Seven to eight years is slow, but it is also squarely in the range the purchasing power parity literature has settled on since Rogoff’s survey put the consensus at three to five years for the real exchange rate, and rather slower than that, which is what you would expect from a single traded good with a large non-traded component.
What I cannot do with these data is say which side does the adjusting.
The index is relative prices minus the nominal exchange rate, and estimating a separate equation for each side requires putting one of them on the right-hand side of the other, where it is endogenous by construction. A regime split would help, since a pegged currency cannot move by definition, but the available classifications describe each currency against its own anchor rather than against the dollar, and half the currencies my model calls pegged are pegged to the euro. That is a question for a different dataset – or a later blog post.
What forty years of burgernomics say
Four findings, in the order of how much weight they will carry.
Prices and exchange rates move together, and that is most of the story. The coefficient on relative prices in an equation for the nominal rate is 0.99, and it is 0.97 when currency fixed effects are added, so it is not an artefact of the pooling.
Deviations from the implied rate revert at 8 to 9% a year. Cassel’s proposition, formulated in 1918 to work out what exchange rates Europe should return to after the war, is the single most robust thing in this data.
Productivity moves the parity, as Balassa and Samuelson said it would. The elasticity is around 0.2. Eight of ten measures give it, from output per hour to total factor productivity to how long people live. The coefficient survives currency and vintage effects.
This is the correction to Cassel, and it is a real one, but it operates on the residual and not on the main relation.
Institutions probably matter and I cannot prove it. Ten institutional measures from two independent sources all carry the predicted sign, and three are individually significant. That consistency is worth something. But add currency fixed effects and the coefficient changes sign, as the model section showed. Institutional quality also correlates 0.75 with productivity, and no amount of econometrics on 55 currencies will separate the two.
And the index is not a currency forecast. It measures the consistency between a country’s price level and its exchange rate, and when the two are out of line the historical record says the gap takes seven or eight years to close. The model cannot say which side gives. A currency 40% from its implied rate is not a prediction that the currency will move 40%.
That last point is the one I would press hardest, because it is the one the index is routinely used against.
The Economist has presented it since 1986 as a guide to whether currencies sit at their correct level, and that framing invites the reader to treat a negative number as a trade. It is not. It is a measurement of how expensive one country is relative to another, and it is a rather good one.
So the index deserves a promotion and a demotion at once. As a currency signal it is weak. As an indicator of relative price levels between countries it is one of the longest and most consistent series anyone has.
Which brings me back to where I started – my reply to Brad Setser was right about the mechanism – poorer countries, i.e. countries with relatively lower productivity, have “undervalued” currencies.
A currency that has been cheap for decades is usually a poor country, and China is the clearest case in the data. Condition on Chinese productivity and the yuan sits within a few percent of where this framework puts it, with the sign of the gap flipping depending on which productivity measure goes in. The raw 30% is income, not manipulation.
On its fortieth birthday, then, the index says something rather unfashionable. Cassel was broadly right, Balassa and Samuelson were right about the correction, the yuan is roughly where Chinese productivity puts it.
References
Source data for the index are published by The Economist in its big-mac-data repository and are the basis for everything here.
• Balassa, B. (1964), “The Purchasing-Power Parity Doctrine: A Reappraisal”, Journal of Political Economy 72(6)
• Cassel, G. (1918), “Abnormal Deviations in International Exchanges”, Economic Journal 28(112)
• Feenstra, R. C., Inklaar, R., and Timmer, M. P. (2015), “The Next Generation of the Penn World Table”, American Economic Review 105(10). Version 11.0 is used here, covering 185 countries to 2023, published in October 2025
• Rogoff, K. (1996), “The Purchasing Power Parity Puzzle”, Journal of Economic Literature 34(2)
• Samuelson, P. A. (1964), “Theoretical Notes on Trade Problems”, Review of Economics and Statistics 46(2)
Data
| Series | Source | Coverage |
| Big Mac prices and exchange rates, 1986-1999 | The Economist, historical source data, via Kaggle | 341 observations, 41 countries |
| Big Mac prices and exchange rates, 2000-2025 | The Economist, source data v2, via Kaggle | 2,302 observations, 73 countries |
| Big Mac full index, January 2026 | The Economist, big-mac-data repository | 54 countries |
| Big Mac dollar prices, July 2026 | The Economist, July 2026 edition | 19 countries, read from the published chart |
| Income at constant PPP prices, inflation, growth | IMF World Economic Outlook | 209 countries, 1980-2030 |
| Productivity, hours worked, TFP, human capital | Penn World Table 11.0 | 185 countries, 1950-2023 |
| Legal system, business regulation, credit market regulation | Fraser Institute, Economic Freedom of the World 2025 | 165 countries, 1970-2023 |
| Life expectancy, schooling, human development index | UNDP, Human Development Report | 195 countries, 1990-2021 |
| Governance indicators | World Bank, Worldwide Governance Indicators | 214 countries, 1996-2023 |
The Fraser index and the Penn World Table both end in 2023. For those series the last observation is carried forward. The main model uses only the Big Mac index, IMF income at constant PPP prices, and the governance indicators.












