Measuring the significance of an FTA partner

Daniel Altman uses a misleading metric to describe the US-Korea trade deal, and I’ve seen this fallacy deployed by a number of others discussing FTAs:

Why is it so important? South Korea ranks just behind the European Union, United States, Japan, China and Hong Kong as an exporter. It shipped $284 billion worth of merchandise in 2005, the last year for which the WTO offers global statistics. That amount, which was three times India’s exports, was also equivalent to the total merchandise shipped by the world’s bottom 118 economies, ranked by the same metric.

All but 30 of those economies are also members of the WTO. So signing a free trade agreement with South Korea could be as economically important as signing agreements with 88 of the group’s 150 members. Given the intense and growing trade relationship between the United States and South Korea, it could be even more important.

Trade agreements are supposed to spur new trade, not entitle partners to claiming the existing volume of trade. (Though the latter might be a rough description of trade diversion.) If the US-Korea FTA doesn’t create any new trade, then it doesn’t matter at all that South Korea is already a massive exporter. Present performance is not a measure of potential gains.