I'm taking the paper on Galton down until David and I sort out the argument better. James Surowiecki is has pointed to a key error in the original sketch -- since, as he notes, Galton did in fact compute the mean. At this point we're considering what part of the argument to hold onto and what will need to change. We've emphasized the importance of entry and competition to ensure that work of experts is checked; now we're in the midst of this ourselves. Our apologies to Surowiecki.
One paragraph we'll add to the next version is:
One of Galton’s defenses for the sample median as the vox populi was it that bounds the influence of any individual voter. Replication and checking of the work of experts may be a way to bound the influence of experts. It is important for the reader to know that in an earlier version we denied the existence of Galton’s mean. This emphasizes the importance of replication and competition precisely to bound the influence of such error.
Here’s what we are prepared to defend :
The majority-rule context of Galton’s publications is lost when the sample median, upon which Galton put such stress, is no longer reported.
Robin Hanson's Overcoming Bias has more comments by Surowiecki and Levy and Peart.