Auction Guessing 1 (Part 2): Fallibility of Christie's and Sotheby's?

As you might imagine, my estimates for the works sold at Christie's were off by a substantial amount. The ratio of the actual price to the estimate provided by the auction house at Christie's was higher than at Sotheby's for two artists but lower for the third. If we assume that the market for Latin-American Art in New York City is fairly integrated, an assumption I believe is reasonable, what does it mean that their estimates were off in different ways?

I had assumed that the comparison between the actual prices and the estimates of the painting for both auction houses would simply reveal the difference between how the current market values the work and the "essential" or inherent value of the work.  But unless the demand for two of the artists increased drastically overnight while demand for the third dropped (possible?), it simply reminds us that no matter how knowledgeable one is, it is impossible to accurately determine an "essential" price.  Does this suggest there is no inherent value, only the value placed by the market?

Auction Guessing 1: Estimating the Results of Christie's Latin American Auction Based on Sotheby's

Sotheby's recently concluded its 2011 auction of Latin American art, with sessions on the 25th at 7 p.m. and the 26th at 10 a.m. In this post I use the results of that auction to estimate the forthcoming results of Christie's Latin American art auction, which has sessions on the 26th at 6:30 pm (NY time) and the 27th at 10 a.m.

I apply a very basic model based on the sold price/mean estimate ratio of works by specific artists, just to see how this compares to the eventual results. After the auction I will compare these revised estimates with their actual price.