Archive for the 'International trade' Category

Dec 04 2013

Planet Money’s t-shirt, comparative advantage and protectionism. A lesson in International Trade

A while back the team behind my favorite podcast, Planet Money, decided to make a t-shirt. In the process, they would tell the whole story of how a t-shirt is made in our global economy. They would track the production of the shirt from the fields where the cotton was grown to the plant where it was spun into thread to the factory where the cloth was cut and stitched into a finished t-shirt.

To finance the story, the Planet Money team undertook a Kickstarter crowd-financing campaign, hoping to get 4,000 listeners like myself to contribute $25 each to help pay for the production of the shirt and the reporting of said production. In the end, over 25,000 listeners supported the campaign, raising nearly $600,000 for the team to pursue its dream of making and telling the whole story behind it!

Along the way they’ve told many great stories about the people and resources that have gone into their shirt, and just this week they released an interactive documentary about the whole project, start to finish. On Sunday evening, after experiencing the documentary, I was inspire to create a lesson for my year 2 IB Economics students, who happen to be studying International Trade (section 3 of the IB course), at this very moment. Below is that lesson, which they are working on this week.

Introduction: The purpose of this activity is to reflect on the principle of comparative advantage and better understand how the patterns of global trade are shaped by this fundamental concept. You will watch and read the story of a t-shirt that was manufactured using resources from four separate countries. Next, you will respond to an essay prompt. Your answer will be graded as a minor assessment.


  1. Read the page that tells the backstory to the Planet Money t-shirt project.
  2. Watch the five part documentary as a class
  3. Read the stories behind the t-shirt’s different stages of production:

Respond to the essay prompt below. (You may begin working on your response while reading the pages above). Your response is due at the beginning of next class and will be graded as a “minor assessment”.

Essay prompt:

A comparative advantage exists when a particular task can be done or a good can be produced at a lower opportunity cost by one nation than by a potential trading partner. When countries specialize in the goods for which they have a comparative advantage, the allocation of resources (land, labor and capital) between nations is more efficient, allowing for a greater level of overall production and income than what is possible without trade.

Carefully explain how the the story of the production of the Planet Money t-shirt demonstrates the principle of comparative advantage. (450 words maximum)

Bonus readingProtectionism and the Planet Money t-shirt

In the above post on the Planet Money blog (made December 2), we learn about the impact that tariffs had on the production of the Planet Money t-shirt.

As you saw in the documentary, the men’s shirt was made in Bangladesh, while the women’s was made in Columbia. We also learned that the Columbian textile worker earn about 3 times as much as the Bangladeshi workers. Why, you may ask, didn’t the ladies’ shirts get made in Bangladesh too? The answer has to do with two “P’s”: productivity and protectionism.

First productivity: According to this podcast, from a week ago, in the Bangladeshi factory where the men’s t-shirt was made, 32 workers on an assembly line would produce 80 t-shirts per hour. In Columbia, on the other hand, 8 workers could produce 140 t-shirts per hour. A simple calculation reveals that the productivity, measured in t-shirts per hour per worker, in the two countries is:

  • Bangladesh: 80/32 = 2.5 t-shirts per hour per worker
  • Columbia: 140/8 = 17.5 t-shirts per hour per worker

The Columbian workers, despite being paid three times the monthly wage that Bangladeshis are making, are 7 times more productive. What accounts for this productivity? Generally, increased productivity is the result of the integration of better or more technology and better training or education among workers. In a low-skilled manufacturing industry like garments, the greater productivity is almost certainly due to greater access to technology in Columbia than in Bangladesh.

On to the second “P”, protectionism: According to this post, due to Columbia’s free trade agreement with the United States, textiles, and most other goods, can be imported into the US “duty-free”, meaning there are no tariffs (import taxes) imposed on Columbian produced goods. This compares to textiles from Bangladesh, on which a 16% tariff is imposed, adding significantly to the cost of producing goods there.

So, let’s put all this together and weigh the advantages and disadvantages of producing t-shirts in the two countries:

In Bangladesh:

In Columbia:

Ironically, while Columbia enjoys certain advantages as a trade partner with the US with high productivity, it appears that the garment industry is slowly disappearing there, as economic development and growth drives up the wage rate further, leading to the country losing its comparative advantage in textile production. Even duty-free status with the US may not allow Columbia to continue to produce t-shirts in the future, as the lower wages of even less developed countries like Cambodia, Laos and yes, even Bangladesh, are too tempting for the garment industry to resist.

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Nov 25 2013

A mathematical proof of the Marshall Lerner Condition

One of the toughest topics to teach in IB higher level Economics is the Marshall Lerner Condition, which is an International Economics concept which states the following:

If the combined price elasticities of demand of a nation’s imports and exports is greater than one (PEDx + PEDm > 1), then a depreciation or a devaluation of the nation’s currency will move its current account balance towards surplus.

This is a concept I have been teaching for eight years now, and I have even written about it in my textbook and produced a YouTube video lecture explaining it to students, but one thing I’ve never done is attempted a mathematical proof of the concept (needless to say, I avoid using math as much as possible, and the prospect of “proving” the MLC was always too daunting).

But this evening I received an email from an Economics teacher in Paris asking for just such a proof. So I buckled down and worked it out. In her email, the teacher said:

The Marshall Lerner Condition states that if the PEDx + PEDm > 1 then a depreciation in a country’s currency will reduce a current account deficit.

Suppose the PED for exports = .6 and the PED for imports = .5. The sum is greater than 1, therefore the MLC is met. A depreciation of this country’s currency should therefore improve its current account balance.

But based on my analysis, this country’s current account should be getting worse, not better.

For Exports: price is decreasing but the quantity demanded is increasing by proportionally  less (since PEDx = 0.6) so the country’s total export revenue is decreasing

For Imports: price is increasing and quantity demanded is decreasing by proportionally less (since PEDm = 0.5) so the country’s total spending on imports is increasing

The country’s revenues from exports are decreasing while the country’s spending on imports are increasing, so overall the trade balance is getting worse (moving deeper into deficit) not improving.

What am I doing wrong?

This teacher’s email really stumped me at first, because her logic is totally sound. I figured the only way I was going to be satisfied was if I worked it mathematically. So here’s the result and the reply I sent to the teacher:


Your email really got me thinking about this. Your logic stumped me at first, but then inspired me to go work it out with numbers. So, hopefully my “proof” of the MLC below will clarify your confusion.

To simplify the analysis we will use easy numbers. I will use your values of PEDx = 0.6 and PEDm = 0.5


  • The US and Canada are trading partners
  • Current exchange rate: $1 US = $1 CA
  • US exports 10 widgets at $1 US apiece for a total export revenue of $10 US
  • US imports 10 wingdings at $1 CA apiece for a total import expenditure of $10 US
  • US trade balance: $10 – $10 = 0
  • PEDx = 0.6 and PEDm = 0.5

Next, assume the US $ depreciates by 10% against the CA $. Now,

  • $1 US = $0.90 CA
  • $1 CA = $1.11 US

Impact on imports:

  • Price to Americans of Canadian wingdings rises to $1.11 US
  • Quantity demanded falls by 5.5% to 9.45
  • Total expenditures on Canadian imports expressed in US $: $1.11 x 9.45 = $10.49

In order for the US trade balance to improve US export revenues must increase by more than $0.49 US.

Impact on exports:

  • Price to Canadians of US widgets falls by 10% to $0.90 CA
  • Quantity demanded increases by 6% to 10.6
  • Total revenue from exports to Canada expressed in CA $: $0.90 x 10.6 = $9.54 CA.
  • Since $1 CA = $1.11 US, the value of US exports to Canada expressed in US $ is $9.54 x $1.11 = $10.59

Expressed in US $, exports increased by $0.59 and imports increased by $0.49.

Therefore, US net exports are now $10.59 – $10.49 = $0.1. The MLC is met and the US trade balance moves into surplus.

I think the only mistake with the logic you applied in your email was that you were not considering that a country’s balance of trade is measured in its own home currency. As you can see, if we measured the value of US exports following the depreciation in Canadian dollars, the export revenues actually decreased following the depreciation of the US $, moving the US into a current account deficit. But even though Canadians are spending less of their own dollars on US goods, the Canadian dollar has now appreciated by 11%, therefore the value of US exports expressed in US $ actually increases (due to the now weaker US $)!

I hope this all makes sense! Thanks for inspiring me to buckle down and tackle this analysis! I’ve been teaching this concept for eight years and have never actually taken the time to walk through a proof like this.


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Feb 07 2013

Lesson plan: Elasticity, exchange rates and the balance of payments – understanding the Marshall Lerner Condition

Related Unit: IB Economics Unit 4.7 – Balance of Payments (Unit 3.3 in the new IB Economics syllabus)

Topic: The Marshall Lerner Condition and the J-Curve

Learning Goals/Objectives:

Test of prior knowledge:

  1. Define ‘price elasticity of demand’ and explain how it is measured.
  2. With the use of examples, explain why some products have low price elasticity while others have a high elasticity. With the use of examples, explain why the price elasticity of demand for some goods changes over time
  3. Explain how the depreciation of a country’s exchange rate might affect its current account balance. IS THIS ALWAYS THE CASE?
  4. How might the PED for exports and imports influence the balance on the current account following a change in the value of a nation’s currency?

Part 1:

The exchange rate of Japanese Yen in the United States over the last two years:

Take a snapshot of your two-year exchange rate diagram in OneNote, then copy and paste the questions below into the page.

Questions to answer in OneNote:

  1. Write a brief description of the changes in your country’s exchange rate over the last two years. (2 marks)
  2. Focus on two specific time periods from during the last two years: One in which your currency appreciated noticeably and one in which it depreciated noticeably. These could be periods of just a couple of days or longer periods of weeks or more. Highlight these in two different covers in your graph.
  3. Describe what is happening to your currency during the two time periods you highlighted in your chart. (2 marks)
  4. Explain TWO factors that may have caused the currency to change in value. (2 marks)
  5. Given the changes to the exchange rate you identified above, what would you predict would happen to your country’s current account balance over the two periods identified? Explain. Following appreciation – in the short-run and in the long-runFollowing depreciation – in the short-run and in the long-run. (4 marks)
  6. Why does the price elasticity of demand for imports and exports increase over time following a change in a country’s exchange rate? (2 marks)
  7. Draw a J-Curve showing the likely change in your nation’s current account balance following the period of depreciation of its currency shown in your chart above and explain its shape, referring to your country’s currency. (2 marks)
  8. For both the period of appreciation and the period of depreciation you identified above, explain the impact of the change in exchange rates on the following (4 marks)
    • a firm that imports its raw materials from the other country
    • a firm that exports its finished products to the other country
    • consumers who buy imports from the other country
    • a firm that produces good for the domestic market and competes with firms from the other country

Part 2:

Read the following article:  How Far Will the Dollar Fall?’ by Richard W. Rahn. Based on the extracts below, answer the questions that follow.

Some applaud the dollar’s fall because they believe it makes U.S. exports less expensive and that higher demand will cut the trade deficit. The downside of a low-value dollar is that it makes all the imports we consume more expensive, including raw material and parts used by U.S. businesses, and makes it costlier for U.S. dollar holders to travel or invest outside the U.S. A continued drop in the dollar’s value could destabilize the international economy, leading to a worldwide recession.

  • Why might the weaker dollar worsen the US trade deficit? Under what conditions would the weaker dollar improve America’s trade deficit? (2 marks)

Some argue our large trade deficit (or current account deficit) is responsible for the fall in the dollar’s value. They have it backward. It is the flow of foreign investment dollars (the capital account) into the U.S. economy that drives the trade deficit.

The world now is actually on a two-currency standard — the dollar and the euro. China in effect has fixed its currency to the dollar for the last two decades, and the Japanese central bank only allows the yen to fluctuate within a limited range against the dollar.

  • How do exchange rate controls by China and Japan reduce the likelihood that a weaker dollar will improve the United States’ current account balance? (2 marks)

So long as the U.S. continues to offer a higher return on capital than its foreign competitors, both foreign banks’ and private investors’ demand for dollars grow, and the current account deficit can be sustained.

  • If investments in the United States began earning lower returns relative to investments in other countries’ financial and capital markets, what would ultimately happen to the US balance of payments in its current and financial accounts? Explain (2 marks)

The above lesson was inspired by the Biz-Ed activity “International Trade: The Falling Dollar or Rising Pound?”

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Mar 06 2012

Planet Money Podcast – “China’s Giant Pool of Money”

NPR’s Planet Money team did a great podcast last week about China’s accumulation of US dollars from its large trade surplus with the United States. This story offers a great illustration of the theories I introduced in my recent video lesson, The Relationship between the Current Account Balance and Exchange Rates

Listen to the podcast, watch the video lesson, and respond to the discussion questions that follow.


Discussion Questions:

  1. Why does the Chinese Central Bank possess over $3 trillion of foreign exchange reserves?
  2. What does the Chinese Central Bank do with the vast majority of the money it earns from the sale of its exports that it does NOT spend on US goods? Why not keep this money in cash?
  3. Why does the Chinese Central Bank manage the value of its currency, the RMB? Why not let the exchange rate be determined by the free market?
  4. As the RMB is slowly strengthened against the dollar, who are the winners and losers? What impact should a stronger RMB have on the balance of trade between China and the US?


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Feb 27 2012

A closer look at Apple’s iPad and iPhone – “made in America”?

I have two  interesting stories on Apple and the iPad to reflect on today.

First, ABC’s Nightline recently became the first Western journalists actually welcomed into an Apple assembly plant in China. The show recently aired a 15 minute feature on working conditions inside Apple’s Foxconn factory in Shenzhen, China last week. Watch the video and then scroll down for what may be some additional surprising news about Apple’s operations in China.

Next, the story that has gone unreported lately is a University of California study titled “Capturing Value in Global Networks: Apple’s iPad and iPhone”. The study’s most interesting finding, in my opinion, is the tiny percentage of the total value of Apple’s iPhone and iPad that actually goes to the Chinese manufacturers of the products. The charts below, from the study, show how the value is divided among the various groups involved it their production and sales:

The Economist provides the analysis:

The chart shows a geographical breakdown of the retail price of an iPad. The main rewards go to American shareholders and workers. Apple’s profit amounts to about 30% of the sales price. Product design, software development and marketing are based in America. Add in the profits and wages of American suppliers, and distribution and retail costs, and America retains about half the total value of an iPad sold there. The next biggest gainers are South Korean firms like Samsung and LG, which provide the display and memory chips, whose profits account for 7% of an iPad’s value. The main financial benefit to China is wages paid to workers for assembling the product and for manufacturing some inputs—equivalent to only 2% of the retail price.

A student today asked why Apple doesn’t produce its products in the United States, where an economic downturn has left 14 million American out of work for the last three or four years. If iPads and iPhones were just made in America, jobs could be created, households would have more income to spend on Apples products, and both the country and the economy would benefit.

The data in the UC study indicates that in fact, more than half the value of an iPad or iPhone does end up in the hands of Americans. But Apple could never achieve the low costs and high profits that it does by assembling its products in the US. After watching the Nightline video above, it should be clear that the type of production involved in Apple factories’ is very low-skilled and labor-intensive. Using American labor, with its unions, minimum wages and 40 hour work weeks, would require Apple to employ such large numbers of workers and raise the company’s variable cost to such a level that the firm’s profits would be reduced significantly and its sales would fall dramatically. Apple would lose out to foreign producers of smart phones and tablet computers, such as LG, Samsung, Sony and others, which would continue assembling their goods with Chinese labor.

Ultimately, any gain to the low-skilled American workers (presuming Apple could even find enough to do the work of the 400,000 Chinese employed in the production of Apple products in China), would be offset by a loss of profits enjoyed by the millions of Americans who hold shares in Apple Computer and the thousands of American who are employed engineering and designing its products, as the firm’s sales would slip in the face of lower-cost competitors.

So this student’s question identifies an interesting paradox: America, with its large pool of unemployed workers, will never be attractive as a place to produce labor-intensive products such as phones and tablet computers, due to the vast wage differential between the US and China. And even if one firm did decide to produce its products in America, the gains to low-skilled workers who may find minimum wage work in the new assembly plants would be off-set by losses to the firms’ shareholders and the high-skilled workers whose jobs would be lost as sales decline due to the lower prices offered by lower-cost competitors.

The lesson here is two-fold: First, Apple and other American technology companies should continue using Chinese labor to assemble their products, and second, America is better off for it: lower costs mean cheaper products and higher sales, thus greater employment in the high-skilled sectors of the US economy, and more profits and returns on the investments of shareholders in American corporations. Americans are richer and enjoy a higher standard of living thanks to the millions of Chinese working in factories assembling the goods we consume.

Keep in mind, this analysis did not even consider the effect on the Chinese economy and the millions of Chinese workers (whose lives are much harder than the typical American) should companies like Apple shut down their Chinese manufacturing plants. That’s a whole other blog post!

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