"In the art market, repeat sales account for a fairly small fraction of total sales. ... Thus, any art index based on repeat sales—such as the Mei-Moses index—is unlikely to be considered representative of any market segment."

Sotheby's has bought the Mei Moses art index, for an undisclosed price.  I'm with Columbia Business School's Arturo Cifuentes, quoted in the header above.  As Felix Salmon put it several years ago, the index is "a creature of massive survivorship bias. The Mei Moses index looks at auction pairs: works of art which have been sold at auction twice. This method gives a very good idea of what has happened to the value of any given work of art over time, but it’s a very bad way of determining what has happened to the art market as a whole, since the kind of works which get auctioned multiple times are decidedly not representative of the broader art world."