How do Amazon and Netflix and other websites know what to recommend? Joseph A. Konstan and John Riedl reveal that a significant feature is knowing what to avoid suggesting:
At their most basic level, these systems avoid what’s known as the supermarket paradox. For example, nearly everyone who walks into a supermarket likes bananas and will often buy some. So shouldn’t the recommender simply recommend bananas to every customer? The answer is no, because it wouldn’t help the customer, and it wouldn’t increase banana sales. So a smart supermarket recommender will always include a rule to explicitly exclude recommending bananas.
That example may sound simplistic, but in one of our early experiences, our system kept recommending the Beatles’ “White Album” to nearly every visitor. Statistically this was a great recommendation: The customers had never purchased this item from the e-commerce site, and most customers rated it highly. And yet the recommendation was useless. Everyone who was interested in the “White Album” already owned a copy.