Spread of Correlation

I was just reading Discover magazine (March, 2008) and came across a review of a book that looks very cool. It's On Being Certain: Believing You Are Right Even When You're Not by Robert A Burton.

I immediately went to amazon.com to put it on my wish list.

Then amazon brought me to the page where it shows you other things bought by people who bought the book you just looked at. I saw another interesting-looking book: Big Brain: The Origins and Future of Human Intelligence by Gary Lynch and Richard Granger. Right up my alley.

I went back to reading Discover to find that this Big Brain book was reviewed on the same page. It struck me, for the first time, that the proximity of the book reviews in some media (magazine, podcast, radio interview, etc.) might actually cause people who buy one book to buy the second. Then this correlation gets reported on amazon. Fascinating!