… is from page 49 of the 2015 Fourth Edition of Dartmouth economist Douglas Irwin’s excellent book, Free Trade Under Fire  (footnote deleted; link added):
Is there systematic evidence that tariffs reduce the range of consumer and intermediate varieties available to an economy? Can we be sure that this reduction in variety of goods is costly to economic welfare? A growing body of evidence suggests that the answer is yes. For example, over the past three decades, the number of varieties imported by the United States has increased by a factor of four. The number of countries supplying each imported good has doubled. As a result, according to one study , consumer welfare is about 2.6 percent of GDP higher over this period [1972-2001] simply due to the gains from variety.