interesting: How Netflix comes up with recommendations for you.

mominatrix

Friday, April 6, 2012

Netflix Recommendations: Beyond the 5 stars (Part 1)

by Xavier Amatriain and Justin Basilico (Personalization Science and Engineering)

 

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Everything is a Recommendation

We have discovered through the years that there is tremendous value to our subscribers in incorporating recommendations to personalize as much of Netflix as possible. Personalization starts on our homepage, which consists of groups of videos arranged in horizontal rows. Each row has a title that conveys the intended meaningful connection between the videos in that group. Most of our personalization is based on the way we select rows, how we determine what items to include in them, and in what order to place those items.

Take as a first example the Top 10 row: this is our best guess at the ten titles you are most likely to enjoy. Of course, when we say ?you?, we really mean everyone in your household. It is important to keep in mind that Netflix? personalization is intended to handle a household that is likely to have different people with different tastes. That is why when you see your Top10, you are likely to discover items for dad, mom, the kids, or the whole family. Even for a single person household we want to appeal to your range of interests and moods. To achieve this, in many parts of our system we are not only optimizing for accuracy, but also for diversity.

Another important element in Netflix? personalization is awareness. We want members to be aware of how we are adapting to their tastes. This not only promotes trust in the system, but encourages members to give feedback that will result in better recommendations. A different way of promoting trust with the personalization component is to provide explanations as to why we decide to recommend a given movie or show. We are not recommending it because it suits our business needs, but because it matches the information we have from you: your explicit taste preferences and ratings, your viewing history, or even your friends? recommendations.

On the topic of friends, we recently released our Facebook connect feature in 46 out of the 47 countries we operate ? all but the US because of concerns with the VPPA law. Knowing about your friends not only gives us another signal to use in our personalization algorithms, but it also allows for different rows that rely mostly on your social circle to generate recommendations.


Some of the most recognizable personalization in our service is the collection of ?genre? rows. These range from familiar high-level categories like "Comedies" and "Dramas" to highly tailored slices such as "Imaginative Time Travel Movies from the 1980s". Each row represents 3 layers of personalization: the choice of genre itself, the subset of titles selected within that genre, and the ranking of those titles. Members connect with these rows so well that we measure an increase in member retention by placing the most tailored rows higher on the page instead of lower. As with other personalization elements, freshness and diversity is taken into account when deciding what genres to show from the thousands possible.

We present an explanation for the choice of rows using a member?s implicit genre preferences ? recent plays, ratings, and other interactions --, or explicit feedback provided through our taste preferences survey. We will also invite members to focus a row with additional explicit preference feedback when this is lacking.


Similarity is also an important source of personalization in our service. We think of similarity in a very broad sense; it can be between movies or between members, and can be in multiple dimensions such as metadata, ratings, or viewing data. Furthermore, these similarities can be blended and used as features in other models. Similarity is used in multiple contexts, for example in response to a member's action such as searching or adding a title to the queue. It is also used to generate rows of ?adhoc genres? based on similarity to titles that a member has interacted with recently. If you are interested in a more in-depth description of the architecture of the similarity system, you can read about it in this past post on the blog.

In most of the previous contexts ? be it in the Top10 row, the genres, or the similars ? ranking, the choice of what order to place the items in a row, is critical in providing an effective personalized experience. The goal of our ranking system is to find the best possible ordering of a set of items for a member, within a specific context, in real-time. We decompose ranking into scoring, sorting, and filtering sets of movies for presentation to a member. Our business objective is to maximize member satisfaction and month-to-month subscription retention, which correlates well with maximizing consumption of video content. We therefore optimize our algorithms to give the highest scores to titles that a member is most likely to play and enjoy.

Now it is clear that the Netflix Prize objective, accurate prediction of a movie's rating, is just one of the many components of an effective recommendation system that optimizes our members enjoyment. We also need to take into account factors such as context, title popularity, interest, evidence, novelty, diversity, and freshness. Supporting all the different contexts in which we want to make recommendations requires a range of algorithms that are tuned to the needs of those contexts. In the next part of this post, we will talk in more detail about the ranking problem. We will also dive into the data and models that make all the above possible and discuss our approach to innovating in this space.

 

 

there's more here:

http://techblog.netflix.com/2012/04/netflix-recommendations-beyond-5-stars.html