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Evaluation of Recommender Algorithms for an Internet Information Broker based on Simple Association Rules and on the Repeat-Buying Theory WEBKDD 2002 Edmonton,

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Presentation on theme: "Evaluation of Recommender Algorithms for an Internet Information Broker based on Simple Association Rules and on the Repeat-Buying Theory WEBKDD 2002 Edmonton,"— Presentation transcript:

1 Evaluation of Recommender Algorithms for an Internet Information Broker based on Simple Association Rules and on the Repeat-Buying Theory WEBKDD 2002 Edmonton, Alberta, Canada Michael Hahsler Andreas Geyer-Schulz

2 Page 2 Michael Hahsler WEBKDD 2002, Edmonton, Canada Introduction Research questions – Are frequent itemsets (association rules) useful to build recommender systems for information brokers? – How does a recommender based on association rules perform compared to a recommender based on the repeat-buying theory known from marketing research? Framework for evaluation Item-to-item correlation type recommender Association rules / Repeat-buying theory Experimental setup Results and conclusion

3 Page 3 Michael Hahsler WEBKDD 2002, Edmonton, Canada Framework for Evaluation added (Fayyad et al. 1996)

4 Page 4 Michael Hahsler WEBKDD 2002, Edmonton, Canada Performance Measures for Recommender Algorithms From Machine Learning – Accuracy – Coverage – MAE From Information Retrieval – Precision / recall – F-measure (F1) / E-measure Other measures – Receiver Operating Characteristic (ROC) – Mobasher's R

5 Page 5 Michael Hahsler WEBKDD 2002, Edmonton, Canada Item-to-item Correlation Type of Recommender Recommendations can be based on many sources of information (e.g. Ansari et al 2000): – Expert evaluations – Expressed preferences – Individual characteristics – Item characteristics (content based) – Expressed preferences of other people (collaborative) We analyze non-personalized transactions where items are used together. explicit, observations

6 Page 6 Michael Hahsler WEBKDD 2002, Edmonton, Canada Association Rules (Agrawal et al, 1993) Support-Confidence Framework Model assumptions: none We use only Rules with 1 item in the antecedent for recommendations Criticism: confidence ignores the frequency of the consequent. Other measures of interestingness are – Lift - symmetric measure of co-occurrence (deviation from independence) – Conviction - deviation of the implication from independence

7 Page 7 Michael Hahsler WEBKDD 2002, Edmonton, Canada Repeat-buying Theory (Ehrenberg 1988) Model assumptions: – Stationary (in the analyzed time period) – "Purchases" of items follow independent Poisson processes – Distribution of the parameters follows a Gamma- distribution – Used for panel data for consumer products (scanner data) LSD (NBD) gives the probability that an item (combination of items) is "purchased" 1,2,...,r times by pure chance.

8 Page 8 Michael Hahsler WEBKDD 2002, Edmonton, Canada Repeat-buying Theory (Recommender) Users "purchase" some items more often together than predicted Filter outliers as potential recommendations Outliers Co-occurence of 2 Web pages from out Dept.'s home page in the Web Server's log

9 Page 9 Michael Hahsler WEBKDD 2002, Edmonton, Canada Experimental Setup (Info. Broker) Educational Internet Information Broker for lecture notes, research material, enrollment information,...

10 Page 10 Michael Hahsler WEBKDD 2002, Edmonton, Canada Experimental Setup (Data Set) Available Data: 6 months of transaction data (January - June 2002) Transactions: 25522 Items: 3774 Co-occurrences:114128 Data Set: co-occurrence lists for 300 items randomly selected 9 users from the target group evaluated 1661 co- occurrences 561 "recommend" - 1100 "don't recommend"

11 Page 11 Michael Hahsler WEBKDD 2002, Edmonton, Canada Experimental Setup (Evaluated Data)

12 Page 12 Michael Hahsler WEBKDD 2002, Edmonton, Canada Results (Support for Association Rules) Low support necessary for reasonable recall

13 Page 13 Michael Hahsler WEBKDD 2002, Edmonton, Canada Results (Lift / Conviction) Lift / conviction don't perform sig. better than confidence.

14 Page 14 Michael Hahsler WEBKDD 2002, Edmonton, Canada Results (Precision, Accuracy) Perform better than a random choice Support-Confidence sensitive to misspecification (conf)

15 Page 15 Michael Hahsler WEBKDD 2002, Edmonton, Canada Results (MAE) Support-Confidence sensitive to misspecification (conf) Repeat-buying seems more robust

16 Page 16 Michael Hahsler WEBKDD 2002, Edmonton, Canada Results (Parameter of the Repeat-buying Recommender) Expected error II rate is below the avg. rate (exception thresholds 0, 0.1, 0.2)

17 Page 17 Michael Hahsler WEBKDD 2002, Edmonton, Canada Conclusion Frequent itemsets represent useful recommendations Accuracy >70%, Precision 60-90% Both algorithms perform very similar with adequate parameters. Repeat-buying algorithm seems more robust to misspecification Model assumptions of the repeat-buying theory need to be checked. Datasets from other applications are needed to confirm findings


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