Average most-favored-nation tariffs in the "Quad" (Canada, the European Union, Japan, and the United States) have fallen to about 5 percent. But tariffs more than three times the average most-favored-nation duty are not uncommon in the Quad and have a disproportionate effect on exports of least...

Although average Organisation for Economic Co-operation and Development (OECD) tariffs on imports from the least developed countries are very low; tariffs above 15 percent have a disproportional effect on their exports. Products subject to tariff peaks tend to be heavily concentrated in...