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Click Chain Model in Web Search Fan Guo Carnegie Mellon University 11/29/2014WWW'09, Madrid, Spain

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Chao Liu MSR, ISRC-Redmond Yi-Min Wang MSR, ISRC-Redmond MSR, Cambridge Mike Taylor MSR, Search Lab Anitha Kannan MSR, Cambridge Tom Minka Carnegie Mellon University Christos Faloutsos Joint Work With…

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1/29/2014WWW'09, Madrid, Spain4

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Click Logs Auto-generated data keeping important information about search activity. 51/29/2014WWW'09, Madrid, Spain Rank/PositionURL of DocumentClick 1www.metalwayfestival.com0 2www.maquitec. com0 3www.construmat.com0 4www.hispack.com0 5www.themarket.com0 6www.cursabombers.com0 7www.setegibernau.com0 8www2009.org1 9www.solardecathlon.upe.es0 10www.nxtbook.com/nxtbooks/suny/2009spring0 Query www 2009 Time 21 Apr 2009, 9:01:02

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Problem Definition Given a click log data set, for each query-document pair, compute user-perceived relevance. 61/29/2014WWW'09, Madrid, Spain Rank/PositionDocument IdxClick 110 280 330 470 550 6120 720 851 9420 10200 Querywww 2009 Session Index103 … Document IdxRelevance 1? 2? 3? 4? 5? 6? 7? 8? 9? … Impression Data Click Data

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Relevance Representation 1/29/2014WWW'09, Madrid, Spain7 Excellent Good Fair Bad 01 Click Chain Model 0.75 Previous Click Models Human Judge Integration

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Applications Automated Ranking Alterations Search Engine Performance Metric Calibrate Human Judgment Related Application in Sponsored Search 81/29/2014WWW'09, Madrid, Spain

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Roadmap Motivation and Problem Definition Click Model Basics CCM and Algorithms Experimental Evaluation Related Work and Conclusion 1/29/2014WWW'09, Madrid, Spain9

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1/29/2014WWW'09, Madrid, Spain10

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Eye-Tracking User Study 111/29/2014WWW'09, Madrid, Spain Fixation Heat Map

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Overall: Fixation is biased towards higher ranks, so do the clicks. For each position: fixation/clicks are context dependent. 121/29/2014WWW'09, Madrid, Spain Normal Impression Reversed Impression

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Problem Definition (Recap) Given a click log data set, for each query-document pair, compute user-perceived relevance and the solution should be – Aware of the position bias and context dependency – Scalable to Terabyte data – Incremental to stay updated 1/29/201413WWW'09, Madrid, Spain

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Examination Hypothesis User behavior abstraction: Fixation binary examination variable Click binary click variable A document must be examined before being clicked. 141/29/2014WWW'09, Madrid, Spain

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Examination Hypothesis For each position, P(Click=1) = P(Examination=1) * Relevance Relevance = P(Click=1|Examination=1) The position bias is reflected in the derivation of P(Examination). 151/29/2014WWW'09, Madrid, Spain

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User scans through documents and make decisions in strict linear order. The decision process: E 1, C 1, E 2, C 2,… Essential part of click model: – What is the probability of See Next Doc? Cascade Hypothesis 161/29/2014WWW'09, Madrid, Spain

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Roadmap Motivation and Problem Definition Click Model Basics CCM and Algorithms Experimental Evaluation Related Work and Conclusion 1/29/2014WWW'09, Madrid, Spain17

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The Context Top-10 organic search results only. Query sessions are independent. Semantic info are not used. 1/29/2014WWW'09, Madrid, Spain18 Suggestions Ads Other Elements

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User Behavior Description 1/29/2014WWW'09, Madrid, Spain19 Examine the Document Click? See Next Doc? Done No Yes No Yes See Next Doc? Done No

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C4C4 C3C3 C2C2 C1C1 Click Chain Model 20 R1R1 E1E1 E2E2 R2R2 R3R3 R4R4 E3E3 E4E4 … … … 1/29/2014WWW'09, Madrid, Spain C5C5 R5R5 E5E5

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Why Bayesian? Modeling Benefit: – A principled way of smoothing the relevance estimates; – Offers more flexibility such as computing P(R i >R j ). Computational Benefit: – Avoid iterative optimization procedure in maximum-likelihood estimation 1/29/2014WWW'09, Madrid, Spain21

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Relevance Inference Given a query, and all its click data compute the posterior for each possible j. Let then focus on click probability for a particular session, and look at different cases 1/29/2014WWW'09, Madrid, Spain22

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C4C4 C3C3 C2C2 C1C1 Click Chain Model 23 R1R1 E1E1 E2E2 R2R2 R3R3 R4R4 E3E3 E4E4 … … … 1/29/2014WWW'09, Madrid, Spain C5C5 R5R5 E5E5 Examination Hypothesis Cascade Hypothesis

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C4C4 C3C3 C2C2 C1C1 24 R1R1 E1E1 E2E2 R2R2 R3R3 R4R4 E3E3 E4E4 … … … 1/29/2014WWW'09, Madrid, Spain C5C5 R5R5 E5E5 0101

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C4C4 C3C3 C2C2 C1C1 25 R1R1 E1E1 E2E2 R2R2 R3R3 R4R4 E3E3 E4E4 … … … 1/29/2014WWW'09, Madrid, Spain C5C5 R5R5 E5E5 0101

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C4C4 C3C3 C2C2 C1C1 26 R1R1 E1E1 E2E2 R2R2 R3R3 R4R4 E3E3 E4E4 … … … 1/29/2014WWW'09, Madrid, Spain C5C5 R5R5 E5E5 0101

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C4C4 C3C3 C2C2 C1C1 27 R1R1 E1E1 E2E2 R2R2 R3R3 R4R4 E3E3 E4E4 … … … 1/29/2014WWW'09, Madrid, Spain C5C5 R5R5 E5E5 0101

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C4C4 C3C3 C2C2 C1C1 28 R1R1 E1E1 E2E2 R2R2 R3R3 R4R4 E3E3 E4E4 … … … 1/29/2014WWW'09, Madrid, Spain C5C5 R5R5 E5E5 0101

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Putting them together 291/29/2014WWW'09, Madrid, Spain

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Summary of the Algorithm Initializing (2*10+2) counts for each pair; Go through the click log once and update the counts; Compute parameter values and get β values; Ready to output results (using numerical integration if necessary). 301/29/2014WWW'09, Madrid, Spain

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Sanity Check The algorithm should be – Aware of the position bias and context dependency – Scalable to Terabyte data Single Pass, Linear – Incremental to stay updated Update counts 1/29/201431WWW'09, Madrid, Spain

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Roadmap Motivation and Problem Definition Click Model Basics CCM and Algorithms Experimental Evaluation Related Work and Conclusion 1/29/2014WWW'09, Madrid, Spain32

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Data Set Collected in 2 weeks in July 2008. Preprocessing: – Discard no-click sessions for fair comparison. – 178 most frequent queries removed. Split to training/test sets according to time stamps. 331/29/2014WWW'09, Madrid, Spain

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Data Set After preprocessing: – 110,630 distinct queries; – 4.8M/4.0M query sessions in the training/test set. 341/29/2014WWW'09, Madrid, Spain

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Metric Efficiency: – Computational Time Effectiveness: – With known document identities in the test set, – Using the relevance and parameter learned on the training set, – To do Click Prediction. 1/29/2014WWW'09, Madrid, Spain35 (resort to indirect measure)

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Competitors UBM: User Browsing Model (Dupret et al., SIGIR08) – More parameters – Iterative, more expensive algorithm DCM: Dependent Click Model (WSDM09) – Modeling 1+ clicks per session 1/29/2014WWW'09, Madrid, Spain36

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Results - Time Environment: Unix Server, 2.8GHz cores, MATLAB R2008b. 1/29/2014WWW'09, Madrid, Spain37 CCMUBMDCM 9.8 min333 min5.4 min 1.0340.55

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Results – Perplexity Perplexity: quality of click prediction for each position individually. 381/29/2014WWW'09, Madrid, Spain Random Guess (p H =0.5): 2.00 Best Guess (p H =0.8): 1.65 Ground Truth (Cheating): 1.00

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Results – Perplexity 391/29/2014WWW'09, Madrid, Spain Worse Better

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Results – Perplexity Average Perplexity over top 10 positions. 401/29/2014WWW'09, Madrid, Spain ModelCCMUBMDCM Perplexity1.14791.15771.1590 Equiv. P H 0.03090.03340.0337 Improv.7.5%8.3%

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Results – Log Likelihood Log-likelihood: log of the chance to recover the entire click vector out of 2 10 possibilities. 411/29/2014WWW'09, Madrid, Spain ModelCCMUBMDCM LL-1.171-1.264-1.302 Likelihood0.31000.27190.2826 Improv.9.7%14%

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Results – Log Likelihood 421/29/2014WWW'09, Madrid, Spain Better Worse

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Roadmap Motivation and Problem Definition Click Model Basics CCM and Algorithms Experimental Evaluation Related Work and Conclusion 1/29/2014WWW'09, Madrid, Spain43

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Related Work User behavior study and hypothesis – Eye-tracking Study (Joachims et al., KDD05, ACM TOIS) – Examination Hypothesis (Richardson et al., WWW07) – Cascade Hypothesis (Craswell et al., WSDM08) Other click models – Logistic Regression (Dupret et al., SIGIR08) – Dynamic Bayesian Network (Chapelle et al., WWW09) – Bayesian Browsing Model (KDD09, To appear) 441/29/2014WWW'09, Madrid, Spain

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Conclusion Click Chain Model – A probabilistic approach to interpret clicks. – A Bayesian approach to model relevance. – Both scalable and incremental. Future Directions – Validation/Bucket Test. – Pairwise comparison – More on context dependency 451/29/2014WWW'09, Madrid, Spain

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Thank you :-) 461/29/2014WWW'09, Madrid, Spain

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Abstract/Document Relevance Relevance of Abstract: – Conditional probability of click as defined by examination hypothesis Relevance of Document: – Determines the probability of See Next Doc – A binary random variable (integrated out under CCM) 1/29/2014WWW'09, Madrid, Spain47

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Alt. User Behavior Description 1/29/2014WWW'09, Madrid, Spain48 Examine the Document Click? Relevant? Yes No See Next Doc? Yes

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Results – Perplexity (by Freq) 491/29/2014WWW'09, Madrid, Spain Worse Better

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Examination/Click Distribution 501/29/2014WWW'09, Madrid, Spain

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Predicting First/Last Clicks Root-Mean-Square error in predicting the first/last clicked position for the test data. Two approaches (bias/variance tradeoff): – EXPectation: using the expected value (bias) – SIMulation: drawing sample from the model (variance) 511/29/2014WWW'09, Madrid, Spain

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First Clicked Position 521/29/2014WWW'09, Madrid, Spain

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Last Clicked Position 531/29/2014WWW'09, Madrid, Spain

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A Quick Example Here we are interested in R 3 541/29/2014WWW'09, Madrid, Spain

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A Quick Example Here we are interested in R 3 551/29/2014WWW'09, Madrid, Spain C4C4 C3C3 C2C2 C1C1

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A Quick Example Here we are interested in R 3 561/29/2014WWW'09, Madrid, Spain C4C4 C3C3 C2C2 C1C1 C4C4 C3C3 C2C2 C1C1

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A Quick Example Here we are interested in R 3 571/29/2014WWW'09, Madrid, Spain C4C4 C3C3 C2C2 C1C1 C4C4 C3C3 C2C2 C1C1 C4C4 C3C3 C2C2 C1C1

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A Quick Example Here we are interested in R 3 581/29/2014WWW'09, Madrid, Spain Mean(R 3 ) = 0.52 Std(R 3 ) = 0.22

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