The Math that Won the Netflix Prize
One of the most important insights is that ratings change over time, as the graphs above suggest. For each movie, ratings increase over time—on average nearly 10% over 5 years. The best explanation for this phenomenon is that people are less discriminating when they rent new releases. To rent an older movie, they need more encouragement—some indication that they will like it—so these end up better matched to their tastes.
For an in depth explanation of the math that won the Netlix prize go here.
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