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Analyzing Weighting Schemes in Collaborative Filtering:
     Cold Start, Post Cold Start and Power Users

                         ACM SAC 2012
            Alan Said, Brijnesh J. Jain, Sahin Albayrak
                    {alan, jain, sahin}@dai-lab.de
                            TU-Berlin
Outline

Movie Recommendation
Problem: Popularity Bias
Collaborative Filtering
Similarity Weighting Schemes
Experiments
Results
Conclusion



30.03.2012                      2
Recommender Systems

What they should do:
   Find items which should be of interest to users
   Find items which should be useful to users


What they often do instead:
   Find items which are known by users
   Find items which users would have found anyway




30.03.2012                                           3
Popularity Bias

                                 What is popularity bias?


Some things are more popular than others
      Blockbuster movies1: Pulp Fiction, Inception, etc.
      Best selling books2: Steve Jobs Bio, A Song of Ice
       and Fire, etc.
      Apps3: Angry Birds, Skype, Kindle

1
    : IMDb most popular
2
    : Amazon 2011 best sellers
3
    : Most downloaded Android apps



30.03.2012                                                  4
Popularity Bias




30.03.2012                     5
Popularity Bias

                        ed
                    rat
                hly
         =  hig
      ms
    ite
    lar
  pu
Po




          30.03.2012                           6
Collaborative Filtering

Looks for users who share rating patterns
Use ratings from like-minded users to calculate a
 prediction for the user
Boils down to:



    The most similar users create a neighborhood.
    Those items which are most popular in the neighborhood will be recommended.




30.03.2012                                                                        7
Collaborative Filtering: Similarities

Standard CF approaches do not consider the
 popularity of items when creating neighbor-
 hoods of similar users.
   i.e. not considering the popularity bias.

                                        Percentage of ratings given to
                                         different popularity classes
                                         of movies in the Movielens
                                         10 Million ratings dataset




30.03.2012                                                               8
Collaborative Filtering: Similarities

Standard CF approaches do not consider the
 popularity of items when creating neighbor-
 hoods of similar users.
   i.e. not considering the popularity bias.

                                                Disitribution of ratings
                                                  given to the three
                                                  most popular
                                                  movies in the
                                                  Movielens 10
                                                  Million dataset




30.03.2012                                                                 9
Weighting Schemes




30.03.2012                       10
Experiments

Approach: Test two similarity weighting strat-
 egies in different scenarios on two different
 movie rating datasets.


   Weighting: Linear Inverse & Inverse User frequency


   Datasets: Movielens10M & Moviepilot


   Scenarios: Cold Start, Post Cold Start, Power Users



30.03.2012                                               11
Results




30.03.2012             12
Results

When is it good to use popularity weighting?
                      Movielens 10M


             >20% improvement in Precision




                               Ratings: 1-5 stars




                      ← 30 - 100 items each →       13
30.03.2012
Results

When is it not good to use popularity weighting?
                       Moviepilot


             No significant improvement in Precision




                                 Ratings: 0-10 stars




30.03.2012                                             14
Conclusion

Popular items create a problem for recom-
 mender systems due to favorable bias.
Similarity weighting can lessen the effects of the
  bias
   when the rating scale is “compact”
   when the users have “more than few” and “less than
    many” ratings




30.03.2012                                              15
Ongoing Work

What if lower precision does not mean poorer
 quality?
   Lower precision can be an indicator of new, novel,
     serendipitous recommendations – these will
     produce lower precision values in offline evaluation
   Currently evaluating the quality of recommender
    algorithms based on user feedback, not only
    precision/recall/etc. Values.
   Users and Noise: The Magic Barrier of Recommender
    Systems – UMAP'12
   User satisfaction survey:
   www.dai-lab.de/~alan/survey
30.03.2012                                                  16
Questions?




             Thank You!




30.03.2012                17

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Analyzing Weighting Schemes in Collaborative Filtering: Cold Start, Post Cold Start and Power Users

  • 1. Analyzing Weighting Schemes in Collaborative Filtering: Cold Start, Post Cold Start and Power Users ACM SAC 2012 Alan Said, Brijnesh J. Jain, Sahin Albayrak {alan, jain, sahin}@dai-lab.de TU-Berlin
  • 2. Outline Movie Recommendation Problem: Popularity Bias Collaborative Filtering Similarity Weighting Schemes Experiments Results Conclusion 30.03.2012 2
  • 3. Recommender Systems What they should do: Find items which should be of interest to users Find items which should be useful to users What they often do instead: Find items which are known by users Find items which users would have found anyway 30.03.2012 3
  • 4. Popularity Bias What is popularity bias? Some things are more popular than others Blockbuster movies1: Pulp Fiction, Inception, etc. Best selling books2: Steve Jobs Bio, A Song of Ice and Fire, etc. Apps3: Angry Birds, Skype, Kindle 1 : IMDb most popular 2 : Amazon 2011 best sellers 3 : Most downloaded Android apps 30.03.2012 4
  • 6. Popularity Bias ed rat hly = hig ms ite lar pu Po 30.03.2012 6
  • 7. Collaborative Filtering Looks for users who share rating patterns Use ratings from like-minded users to calculate a prediction for the user Boils down to: The most similar users create a neighborhood. Those items which are most popular in the neighborhood will be recommended. 30.03.2012 7
  • 8. Collaborative Filtering: Similarities Standard CF approaches do not consider the popularity of items when creating neighbor- hoods of similar users. i.e. not considering the popularity bias. Percentage of ratings given to different popularity classes of movies in the Movielens 10 Million ratings dataset 30.03.2012 8
  • 9. Collaborative Filtering: Similarities Standard CF approaches do not consider the popularity of items when creating neighbor- hoods of similar users. i.e. not considering the popularity bias. Disitribution of ratings given to the three most popular movies in the Movielens 10 Million dataset 30.03.2012 9
  • 11. Experiments Approach: Test two similarity weighting strat- egies in different scenarios on two different movie rating datasets. Weighting: Linear Inverse & Inverse User frequency Datasets: Movielens10M & Moviepilot Scenarios: Cold Start, Post Cold Start, Power Users 30.03.2012 11
  • 13. Results When is it good to use popularity weighting? Movielens 10M >20% improvement in Precision Ratings: 1-5 stars ← 30 - 100 items each → 13 30.03.2012
  • 14. Results When is it not good to use popularity weighting? Moviepilot No significant improvement in Precision Ratings: 0-10 stars 30.03.2012 14
  • 15. Conclusion Popular items create a problem for recom- mender systems due to favorable bias. Similarity weighting can lessen the effects of the bias when the rating scale is “compact” when the users have “more than few” and “less than many” ratings 30.03.2012 15
  • 16. Ongoing Work What if lower precision does not mean poorer quality? Lower precision can be an indicator of new, novel, serendipitous recommendations – these will produce lower precision values in offline evaluation Currently evaluating the quality of recommender algorithms based on user feedback, not only precision/recall/etc. Values. Users and Noise: The Magic Barrier of Recommender Systems – UMAP'12 User satisfaction survey: www.dai-lab.de/~alan/survey 30.03.2012 16
  • 17. Questions? Thank You! 30.03.2012 17