Understanding Web Browsing Behaviors through Weibull Analysis of Dwell Time Chao Liu, Ryen White, Susan Dumais Microsoft Research at Redmond

Dwell Time as User Implicit Feedbacks  The most significant indicator of document relevance besides clickthroughs [Kelly and Belkin, SIGIR’01, SIGIR’04]  Leveraged in various applications  Learning to rank [Agichtein et al., SIGIR’06]  Query expansion [Buscher et al., SIGIR’09]  BrowseRank, assuming an exponential dist. [Liu et al., SIGIR’08]  …

Questions Addressed in this Study  Questions:  How do we model the dwell time distribution Pr(t|d)?  What does Pr(t|d) tell us about user browsing behaviors?  How is the distribution related to page-level features, and can we predict the distribution based on page-level features?  Takeaways  We propose to model Pr(t|d) using Weibull distributions  The fitted Weibull distribution exhibits a strong negative aging effect, which indicates a “screen-and-glean” browsing behavior  We can predict Pr(t|d) based on page features, which effectively extends the application of dwell time to scenarios where dwell time data is not available

Outline  A Primer on Weibull Analysis  Weibull distribution and analysis  Hazard function and aging effects  Weibull Analysis on Dwell Time  Goodness-of-Fit  Screen-and-glean browsing pattern  Screening by categories  Predicting Dwell Time Distribution  Prediction performance  Feature importance  Conclusions

Weibull Analysis  Weibull analysis is a method for modeling positive data sets, such as time-to-failure data  Predicting product life,  Comparing reliability of competing product designs  Establishing warranty policies or proactively managing spare parts inventories  Success beyond reliability engineering  Survival analysis, weather forecasting, fading channels in wireless communication, the length of labor strikes, AIDS mortality and earthquake probabilities, etc.  Unfortunately, no prior Weibull analysis on Web data although Web abounds with temporal data  Page dwell time, session length, time-to-first-click, etc

Weibull Distribution  2-parameter Weibull distribution  λ : scale parameter  k: shape parameter  Exponential dist. when k = 1

Weibull Analysis  Hazard function at time x  Instantaneous failure rate (or hazard rate) at time x  Amount of risk associated with an x-survivor at time x  Hazard function for Weibull distributions

Aging Effects from Hazard Function  k = 1: No aging  Constant failure rate  Exponential distribution  0<k<1: Negative aging  Decreasing failure rate  An initial screening has to be passed in order to survive longer  Smaller k means harsher screening  k > 1: Positive aging  Increasing failure rate  Little to no screening at the beginning but life becomes tougher as time goes by

Weibull Analysis on Dwell Time and Beyond  Web abounds with temporal data  Time to first click, session length, eye fixation, …  Weibull analysis is way beyond hazard functions  Failure forecasting, corrective actions, … Reliability Analysis Dwell Time AnalysisClick Analysis… Datatime-to-failureTime-to-abandonTime-to-first-click… HazardFailure rateAbandon rateClick rate… E(t|t>t 0 )Mean residual lifeMean residual time on page How soon to click… ……………

Outline  A Primer on Weibull Analysis  Weibull distribution and analysis  Hazard function and aging effects  Weibull Analysis on Dwell Time  Goodness-of-Fit  Screen-and-glean browsing pattern  Screening by categories  Predicting Dwell Time Distribution  Prediction performance  Feature importance  Conclusions

Goodness-of-Fit Comparison  Dwell time collected for 205,873 pages (URLs) in English (US) market, each of which has a minimum of 10k dwell times  Comparison on Goodness-of-Fit (GoF)  Dwell times for each page are split into training (80%) and testing (20%)  Model fitting on training and evaluated on testing  Metrics: Log-likelihood and Kolmogorov–Smirnov distance

Fitting λ and k Strong Negative Aging What’s the initial screening? Screen-and-glean browsing pattern?

P( k |Category): Aging Effect w.r.t. Categories Screening is harsher for less-entertaining topics

Outline  A Primer on Weibull Analysis  Weibull distribution and analysis  Hazard function and aging effects  Weibull Analysis on Dwell Time  Goodness-of-Fit  Screen-and-glean browsing pattern  Screening by categories  Predicting Dwell Time Distribution  Prediction performance  Feature importance  Conclusions

Dwell Time Prediction from Page Features  Why predicting dwell time?  Extend dwell time to pages with less or no dwell time  Enable third parties to leverage dwell time even if they don’t have access to real dwell time data  Gain insights into what elements affect dwell time  Why using only page-level features?  Users decide how long to stay with a page based on the experience and perception, rather than PageRank for example  Advanced features like PageRank and inlink counts may not be available to all parties

Experiment Setup  5000 randomly sampled pages with fitted λ and k as the target values  Pages are crawled using a dynamic crawler, which parses the html, executes all dynamic components (e.g., redirections, flashes, javascripts, etc), and finally renders the page  “login” pages are removed as they are likely due to time-out redirection  4771 pages left  Page-level features  HtmlTag: frequencies of 93 Html tags  Content: frequencies of top-1000 terms  Dynamic: statistics from dynamic crawling  Regressor: Multiple Additive Regression Tree (MART)  Effectiveness and feature interpretability

Baseline returns the mean λ and k Prediction Results  Comparisons with various feature configurations  Prediction outperforms the baseline  HtmlTag and Dynamic are similar effectively when separated, and complementary to each other when combined  Content > HtmlTag+Dynamic  Content+Dynamic the best: Dynamic captures what users experience after clicks whereas Content shows what users would see in the end

Important Features

Outline  A Primer on Weibull Analysis  Weibull distribution and analysis  Hazard function and aging effects  Weibull Analysis on Dwell Time  Goodness-of-Fit  Screen-and-glean browsing pattern  Screening by categories  Predicting Dwell Time Distribution  Prediction performance  Feature importance  Conclusions

Conclusions  The first Weibull analysis on Web dwell time  Draws an analogy between dwell time and lifetime  Opens the door to Weibull analysis for temporal implicit feedbacks  Dwell time exhibits a strong negative aging effect, which hints a prevalent “screen and glean” browsing pattern  Harsher screening for less-entertaining topics  Feasible to predict dwell time based on page-level features  Extending applicability to less-visited pages and parties without dwell time data  Future work  Improving prediction accuracy through better feature engineering  Weibull analysis for IR

Acknowledgments  Yutaka Suzue  Krysta Svore  Qiang Wu  Wen-tau Yih  Xiaoxin Yin  Alice Zheng

Q&A Thank You!