A long time ago suddenly Amazon started recommending me a lot of medical stuff, like anatomy books, drug dictionaries, etc. Looking at why I was recommended it (which is one of the best features for curious people like me), it was all because I had bought a Palm Pilot (yes, this was a long time ago). Apparently Palm Pilots were very popular among doctors because it had some very useful apps for them to keep track of patients, do quick calculations and get references to drugs.
The interesting thing is that if you think of the statistics of it (and I ask people that claim statistics background to go through this during interviews all the time), it makes sense that you will see something like this if you have a biased population. Let's say that out of customers for product A, 20% are medical doctors and the rest is a random scattering of other types of people. If, just to make it simple, 50% of all medical doctors buy product B, suddenly you will see that 10% of everybody that bought product A also bought product B.
The reason that medical doctors are such an interesting category is that I'm not aware of any other category of people that have such strong counts of specific products they purchase. Engineers don't all buy similar books. Graphic designers also don't. Maybe lawyers might, but I haven't seen any evidence that this is happening.
Anyway, why was this brought to my attention? Well, it's because I added something to my Amazon wedding registry and I received the following recommendation:
A stethoscope? Unfortunately for this type of recommendation I can't see why I was recommended it. It would have been interesting.