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The move represents a diversion from the company’s traditional auctioneering roots but seems part of a strategy of further promoting art as an investment-class asset.

In a statement, Sotheby’s said: “Through this acquisition, Sotheby's has unique access to an analytic tool that provides objective and verifiable information to complement the world-class expertise of the company's specialists.”

Sotheby's Executive Vice President Adam Chinn said:  “The collecting community is increasingly sophisticated and, in many cases, looking to analysis to understand the overall market, individual artist and category trends, the value of their collections, as well as gain insight into the timing of their consignments and purchases."

It will now be known as Sotheby's Mei Moses.

Repeat Sales

In contrast to other art price databases which analyse auction prices, the Mei Moses indices track the values of art by using repeat sales of individual objects – in effect comparing price changes of particular works at different points in time.

Their database of 45,000 repeat sales, which is updated with around 4000 objects changing hands each year, is categorised into eight collecting categories.

Sotheby’s said this methodology has made Mei Moses the “pre-eminent measure of the state of the art market”.

“The methodology enables Sotheby's to compare the investment performance of art against various asset classes, analyse its performance against myriad benchmarks and competitors, and measure the impact of macro-economic and societal forces on the art market,” said the firm.

Examining Trends

However, critics of art market indices would point to the fact that factors such as provenance and market freshness have a significant effect on values but are not represented in number-crunching databases. Another problem comes when works are unsold at auction – an important factor in market performance but not reflected in either auction-price or repeat-sales statistics.

The Mei Moses Art Indices, which was co-founded in 2001 by Michael Moses, a former NYU professor and Jianping Mei, a professor at the Cheung Kong Graduate School of Business in Beijing, examines only data from Sotheby’s and Christie’s.

Chinn said: “We are very happy to be in a position to provide collectors with proprietary information tailored to their needs, while at the same time helping us identify and examine trends that can inspire further innovations within Sotheby's to better serve an expanding client base."

Dealers have often voiced concern that promoting an investment-only approach to buying art could be a poisoned chalice, especially at the expense of long-term collecting which underpins the market.