By PATRICIA COHEN

Ask David Galenson to name the single greatest work of art from the 20th century, and he unhesitatingly answers “Les Demoiselles d’Avignon,” a 1907 painting by Picasso. He can then tell you with certainty Nos. 2, 3, 4, 5 and so on, as well.
His confidence in the ranking doesn’t come from a stack of degrees in art history . After all, Mr. Galenson is an economist at the University of Chicago who initially specialized in colonial America. But during the past 10 years he has turned his attention to artists and creativity, convinced that the type of economic analysis that explains the expensive gas at the pump can also explain the greatest artists of the last 100 or so years.
His approach has led to what he says is a radically new interpretation of 20th-century art, one he is certain art historians will hate. It is based in part on how frequently an illustration of a work appears in textbooks.
“Quantification has been almost totally absent from art history,” he said. “Art historians hate markets.”
To Mr. Galenson markets are what make the 20th century different from other eras for art. In earlier periods artists created works for rich patrons in the court or the church, which functioned as a monopoly. Only in the 20th century did art enter the marketplace and become a commodity .
In this system, he said, breaking the rules became the most valued attribute. The greatest rewards went to conceptual innovators who frequently changed styles and invented genres. For the first time the idea behind the work of art became more important than the physical object itself.
He intends to push his theories further in a forthcoming book, which will take on the entire last century in art. Since many of the most important individual works rarely, if ever, come to market, he decided to use art history textbooks to value each piece. He tallied the number of illustrations of each piece in the 33 textbooks he found that were published between 1990 and 2005, on the assumption that the most important works merited the most illustrations.
“Demoiselles” was No. 1 with 28 illustrations. Vladimir Tatlin’s “Monument to the Third International” (1919- 20), a plan for a celebratory tower, was second with 25 illustrations. “Spiral Jetty,” a gigantic earthwork coil that Robert Smithson planted in the Great Salt Lake in Utah in 1970, was third with 23, followed by Richard Hamilton’s “Just What Is It That Makes Today’s Homes So Different, So Appealing?,” a 1956 collage widely considered to be the first Pop Art, with 22.
Art experts, not surprisingly, are skeptical. “Particularly in a society that values the progressive, there is an instinct to make great and influential the same thing, but they aren’t necessarily,” John Elderfield, chief curator emeritus at the Museum of Modern Art in New York, said when Mr. Galenson’s theory was described to him.
About the ranking, Mr. Elderfield said, “Frankly, it’s preposterous.”