Wolfgang F. Stolper, 89, an economist whose work included a theory used to explain the effect of international trade on wages, died Monday in Ann Arbor, Mich., during surgery to clear a blood clot.

There was a big debate about this in the economics profession in the early 1990s. Not one single economist argued about the direction of trade’s effect ? it was universally agreed that it was negative ...

In a famous theorem, known as Stolper-Samuelson, he and a co-author showed that competition from imports of clothes and similar goods from underdeveloped countries, where producers rely on unskilled ...