An increase in online-only auctions, which generally do not publish price results, along with private sales at auctions houses and sales through galleries and dealers--which make up 53% of the global art market, according to TEFAF's annual report---obscure the market results for many artists.

Forbes' Kathryn Tully shows how different art indices slice and dice the data with an overview of Mei Moses, Artnet, and Artprice.