Editing Comparative advantage (section)

===Direct test: natural experiment of Japan===
Assessing the validity of comparative advantage on a global scale with the examples of contemporary economies is analytically challenging because of the multiple factors driving globalization: indeed, investment, migration, and technological change play a role in addition to trade. Even if we could isolate the workings of open trade from other processes, establishing its causal impact also remains complicated: it would require a comparison with a counterfactual world without open trade. Considering the durability of different aspects of globalization, it is hard to assess the sole impact of open trade on a particular economy.{{Cn|date=August 2021}}

[[Daniel Bernhofen]] and John Brown have attempted to address this issue, by using a natural experiment of a sudden transition to open trade in a market economy. They focus on the case of Japan.{{sfn|Bernhofen|Brown|2004|pages=48–67}}{{sfn|Bernhofen|Brown|2005b|pages=208–225}} The Japanese economy indeed developed over several centuries under autarky and a quasi-isolation from international trade but was, by the mid-19th century, a sophisticated market economy with a population of 30 million. Under Western military pressure, Japan opened its economy to foreign trade through a series of [[unequal treaties]].{{Cn|date=August 2021}}

In 1859, the treaties limited tariffs to 5% and opened trade to Westerners. Considering that the transition from autarky, or self-sufficiency, to open trade was brutal, few changes to the fundamentals of the economy occurred in the first 20 years of trade. The general law of comparative advantage theorizes that an economy should, on average, export goods with low self-sufficiency prices and import goods with high self-sufficiency prices. Bernhofen and Brown found that by 1869, the price of Japan's main export, silk and derivatives, saw a 100% increase in real terms, while the prices of numerous imported goods declined of 30-75%. In the next decade, the ratio of imports to gross domestic product reached 4%.{{sfn|Bernhofen|Brown|2016|pages=54–90}}