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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
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
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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
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6. Popularity Bias
ed
rat
hly
= hig
ms
ite
lar
pu
Po
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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.
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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
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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
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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
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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
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14. Results
When is it not good to use popularity weighting?
Moviepilot
No significant improvement in Precision
Ratings: 0-10 stars
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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
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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
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