Something is fishy with this recommender
In my rather long winded post on the problems with current music recommenders, I pointed out the Harry Potter Effect. Collaborative Filtering recommenders tend to recommend things that are popular which makes those items even more popular, creating a feedback loop - (or as the podcomplex calls it - the similarity vortex) that results in certain items becoming extremely popular at the expense of overall diversity. (For an interesting demonstration of this effect, see 'Online monoculture and the end of the niche').
Oscar sent me an example of this effect. At the popular British online music store HMV, a rather large fraction of artists recommendations point to the Kings of Leon. Some examples:
Oscar points out that even for albums that haven't been released, HMV will tell you that 'customers that bought the new unreleased album by Depeche Mode also bought the Kings of Leon'. Of course it is no surprise that if you look at the HMV bestsellers, The Kings Of Leon is way up there at position #3.
At first blush, this does indeed look like a classic example of the Harry Potter Effect, but I'm a bit suspicious that what we are seeing is not an example of a feedback loop, but is an example of shilling - using the recommender to explicitly promote a particular item. It may be that HMV has decided to hardwire a slot in their 'customers who bought this also bought' section to point to an item that they are trying to promote - perhaps due to a sweetheart deal with a music label. I don't have any hard evidence of this, but when you look at the wide variety of artists that point to Kings of Leon - from Miley Cyrus, to Led Zeppelin and Nirvana it is hard to imagine that this is a result of natural collaborative filtering. Music promotion that disguises itself as music recommendation has been around for about as long as there have been people looking for new music. Payola schemes have dogged radio for decades. It is not hard to believe that this type of dishonest marketing will find its way into recommender systems. We've already seen the rise of 'search engine optimization' companies that will get your web site on the first page of google search results - it won't be long before we see a recommender engine optimizer industry that will promote your items by manipulating recommenders. It may already be happening now, and we just don't know about it. The next time you get a recommendation for The Kings of Leon because you like The Rolling Stones, ask yourself if this is a real and honest recommendation or are they just trying to sell you something.