Recsperts - Recommender Systems Experts Marcel Kurovski

In episode 22 of Recsperts, we welcome Prabhat Agarwal, Senior ML Engineer, and Aayush Mudgal, Staff ML Engineer, both from Pinterest, to the show. Prabhat works on recommendations and search systems at Pinterest, leading representation learning efforts. Aayush is responsible for ads ranking and privacy-aware conversion modeling. We discuss user and content modeling, short- vs. long-term objectives, evaluation as well as multi-task learning and touch on counterfactual evaluation as well.
In our interview, Prabhat guides us through the journey of continuous improvements of Pinterest's Homefeed personalization starting with techniques such as gradient boosting over two-tower models to DCN and transformers. We discuss how to capture users' short- and long-term preferences through multiple embeddings and the role of candidate generators for content diversification. Prabhat shares some details about position debiasing and the challenges to facilitate exploration.With Aayush we get the chance to dive into the specifics of ads ranking at Pinterest and he helps us to better understand how multifaceted ads can be. We learn more about the pain of having too many models and the Pinterest's efforts to consolidate the model landscape to improve infrastructural costs, maintainability, and efficiency. Aayush also shares some insights about exploration and corresponding randomization in the context of ads and how user behavior is very different between different kinds of ads.Both guests highlight the role of counterfactual evaluation and its impact for faster experimentation.
Towards the end of the episode, we also touch a bit on learnings from last year's RecSys challenge.
Enjoy this enriching episode of RECSPERTS - Recommender Systems Experts.Don't forget to follow the podcast and please leave a review

(00:00) - Introduction
(03:51) - Guest Introductions
(09:57) - Pinterest Introduction
(21:57) - Homefeed Personalization
(47:27) - Ads Ranking
(01:14:58) - RecSys Challenge 2023
(01:20:26) - Closing Remarks
Links from the Episode:Prabhat Agarwal on LinkedInAayush Mudgal on LinkedInRecSys Challenge 2023Pinterest Engineering BlogPinterest LabsPrabhat's Talk at GTC 2022: Evolution of web-scale engagement modeling at PinterestBlogpost: How we use AutoML, Multi-task learning and Multi-tower models for Pinterest AdsBlogpost: Pinterest Home Feed Unified Lightweight Scoring: A Two-tower ApproachBlogpost: Experiment without the wait: Speeding up the iteration cycle with Offline Replay ExperimentationBlogpost: MLEnv: Standardizing ML at Pinterest Under One ML Engine to Accelerate InnovationPapers:
Eksombatchai et al. (2018): Pixie: A System for Recommending 3+ Billion Items to 200+ Million Users in Real-TimeYing et al. (2018): Graph Convolutional Neural Networks for Web-Scale Recommender SystemsPal et al. (2020): PinnerSage: Multi-Modal User Embedding Framework for Recommendations at PinterestPancha et al. (2022): PinnerFormer: Sequence Modeling for User Representation at PinterestZhao et al. (2019): Recommending what video to watch next: a multitask ranking systemGeneral Links:
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In episode 21 of Recsperts, we welcome Martijn Willemsen, Associate Professor at the Jheronimus Academy of Data Science and Eindhoven University of Technology. Martijn's researches on interactive recommender systems which includes aspects of decision psychology and user-centric evaluation. We discuss how users gain control over recommendations, how to support their goals and needs as well as how the user-centric evaluation framework fits into all of this.
In our interview, Martijn outlines the reasons for providing users control over recommendations and how to holistically evaluate the satisfaction and usefulness of recommendations for users goals and needs. We discuss the psychology of decision making with respect to how well or not recommender systems support it. We also dive into music recommender systems and discuss how nudging users to explore new genres can work as well as how longitudinal studies in recommender systems research can advance insights.
Towards the end of the episode, Martijn and I also discuss some examples and the usefulness of enabling users to provide negative explicit feedback to the system.
Enjoy this enriching episode of RECSPERTS - Recommender Systems Experts.Don't forget to follow the podcast and please leave a review

(00:00) - Introduction
(03:03) - About Martijn Willemsen
(15:14) - Waves of User-Centric Evaluation in RecSys
(19:35) - Behaviorism is not Enough
(46:21) - User-Centric Evaluation Framework
(01:05:38) - Genre Exploration and Longitudinal Studies in Music RecSys
(01:20:59) - User Control and Negative Explicit Feedback
(01:31:50) - Closing Remarks
Links from the Episode:Martijn Willemsen on LinkedInMartijn Willemsen's WebsiteUser-centric Evaluation FrameworkBehaviorism is not Enough (Talk at RecSys 2016)Neil Hunt: Quantifying the Value of Better Recommendations (Keynote at RecSys 2014)What recommender systems can learn from decision psychology about preference elicitation and behavioral change (Talk at Boise State (Idaho) and Grouplens at University of Minnesota)Eric J. Johnson: The Elements of ChoiceRasch ModelSpotify Web APIPapers:
Ekstrand et al. (2016): Behaviorism is not Enough: Better Recommendations Through Listening to UsersKnijenburg et al. (2012): Explaining the user experience of recommender systemsEkstrand et al. (2014): User perception of differences in recommender algorithmsLiang et al. (2022): Exploring the longitudinal effects of nudging on users’ music genre exploration behavior and listening preferencesMcNee et al. (2006): Being accurate is not enough: how accuracy metrics have hurt recommender systemsGeneral Links:
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In episode 20 of Recsperts, we welcome Bram van den Akker, Senior Machine Learning Scientist at Booking.com. Bram's work focuses on bandit algorithms and counterfactual learning. He was one of the creators of the Practical Bandits tutorial at the World Wide Web conference. We talk about the role of bandit feedback in decision making systems and in specific for recommendations in the travel industry.
In our interview, Bram elaborates on bandit feedback and how it is used in practice. We discuss off-policy- and on-policy-bandits, and we learn that counterfactual evaluation is right for selecting the best model candidates for downstream A/B-testing, but not a replacement. We hear more about the practical challenges of bandit feedback, for example the difference between model scores and propensities, the role of stochasticity or the nitty-gritty details of reward signals. Bram also shares with us the challenges of recommendations in the travel domain, where he points out the sparsity of signals or the feedback delay.
At the end of the episode, we can both agree on a good example for a clickbait-heavy news service in our phones.
Enjoy this enriching episode of RECSPERTS - Recommender Systems Experts.Don't forget to follow the podcast and please leave a review

(00:00) - Introduction
(02:58) - About Bram van den Akker
(09:16) - Motivation for Practical Bandits Tutorial
(16:53) - Specifics and Challenges of Travel Recommendations
(26:19) - Role of Bandit Feedback in Practice
(49:13) - Motivation for Bandit Feedback
(01:00:54) - Practical Start for Counterfactual Evaluation
(01:06:33) - Role of Business Rules
(01:11:26) - better cut this section coherently
(01:17:48) - Rewards and More
(01:32:45) - Closing Remarks
Links from the Episode:Bram van den Akker on LinkedInPractical Bandits: An Industry Perspective (Website)Practical Bandits: An Industry Perspective (Recording)Tutorial at The Web Conference 2020: Unbiased Learning to Rank: Counterfactual and Online ApproachesTutorial at RecSys 2021: Counterfactual Learning and Evaluation for Recommender Systems: Foundations, Implementations, and Recent AdvancesGitHub: Open Bandit PipelinePapers:
van den Akker et al. (2023): Practical Bandits: An Industry Perspectivevan den Akker et al. (2022): Extending Open Bandit Pipeline to Simulate Industry Challengesvan den Akker et al. (2019): ViTOR: Learning to Rank Webpages Based on Visual FeaturesGeneral Links:
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In episode 19 of Recsperts, we welcome Himan Abdollahpouri who is an Applied Research Scientist for Personalization & Machine Learning at Spotify. We discuss the role of popularity bias in recommender systems which was the dissertation topic of Himan. We talk about multi-objective and multi-stakeholder recommender systems as well as the challenges of music and podcast streaming personalization at Spotify.
In our interview, Himan walks us through popularity bias as the main cause of unfair recommendations for multiple stakeholders. We discuss the consumer- and provider-side implications and how to evaluate popularity bias. Not the sheer existence of popularity bias is the major problem, but its propagation in various collaborative filtering algorithms. But we also learn how to counteract by debiasing the data, the model itself, or it's output. We also hear more about the relationship between multi-objective and multi-stakeholder recommender systems.
At the end of the episode, Himan also shares the influence of popularity bias in music and podcast streaming at Spotify as well as how calibration helps to better cater content to users' preferences.
Enjoy this enriching episode of RECSPERTS - Recommender Systems Experts.Don't forget to follow the podcast and please leave a review

(00:00) - Introduction
(04:43) - About Himan Abdollahpouri
(15:23) - What is Popularity Bias and why is it important?
(25:05) - Effect of Popularity Bias in Collaborative Filtering
(30:30) - Individual Sensitivity towards Popularity
(36:25) - Introduction to Bias Mitigation
(53:16) - Content for Bias Mitigation
(56:53) - Evaluating Popularity Bias
(01:05:01) - Popularity Bias in Music and Podcast Streaming
(01:08:04) - Multi-Objective Recommender Systems
(01:16:13) - Multi-Stakeholder Recommender Systems
(01:18:38) - Recommendation Challenges at Spotify
(01:35:16) - Closing Remarks
Links from the Episode:Himan Abdollahpouri on LinkedInHiman Abdollahpouri on XHiman's WebsiteHiman's PhD Thesis on "Popularity Bias in Recommendation: A Multi-stakeholder Perspective"2nd Workshop on Multi-Objective Recommender Systems (MORS @ RecSys 2022)Papers:
Su et al. (2009): A Survey on Collaborative Filtering TechniquesMehrotra et al. (2018): Towards a Fair Marketplace: Counterfactual Evaluation of the trade-off between Relevance, Fairness & Satisfaction in Recommender SystemsAbdollahpouri et al. (2021): User-centered Evaluation of Popularity Bias in Recommender SystemsAbdollahpouri et al. (2019): The Unfairness of Popularity Bias in RecommendationAbdollahpouri et al. (2017): Controlling Popularity Bias in Learning-to-Rank RecommendationWasilewsi et al. (2016): Incorporating Diversity in a Learning to Rank Recommender SystemOh et al. (2011): Novel Recommendation Based on Personal Popularity TendencySteck (2018): Calibrated RecommendationsAbdollahpouri et al. (2023): Calibrated Recommendations as a Minimum-Cost Flow ProblemSeymen et al. (2022): Making smart recommendations for perishable and stockout productsGeneral Links:
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In episode 18 of Recsperts, we hear from Professor Sole Pera from Delft University of Technology. We discuss the use of recommender systems for non-traditional populations, with children in particular. Sole shares the specifics, surprises, and subtleties of her research on recommendations for children.
In our interview, Sole and I discuss use cases and domains which need particular attention with respect to non-traditional populations. Sole outlines some of the major challenges like lacking public datasets or multifaceted criteria for the suitability of recommendations. The highly dynamic needs and abilities of children pose proper user modeling as a crucial part in the design and development of recommender systems. We also touch on how children interact differently with recommender systems and learn that trust plays a major role here.
Towards the end of the episode, we revisit the different goals and stakeholders involved in recommendations for children, especially the role of parents. We close with an overview of the current research community.
Enjoy this enriching episode of RECSPERTS - Recommender Systems Experts.Don't forget to follow the podcast and please leave a review

(00:00) - Introduction
(04:56) - About Sole Pera
(06:37) - Non-traditional Populations
(09:13) - Dedicated User Modeling
(25:01) - Main Application Domains
(40:16) - Lack of Data about non-traditional Populations
(47:53) - Data for Learning User Profiles
(57:09) - Interaction between Children and Recommendations
(01:00:26) - Goals and Stakeholders
(01:11:35) - Role of Parents and Trust
(01:17:59) - Evaluation
(01:26:59) - Research Community
(01:32:37) - Closing Remarks
Links from the Episode:Sole Pera on LinkedInSole's WebsiteChildren and RecommendersKidRec 2022People and Information Retrieval Team (PIReT)Papers:
Beyhan et al. (2023): Covering Covers: Characterization Of Visual Elements Regarding SleevesMurgia et al. (2019): The Seven Layers of Complexity of Recommender Systems for Children in Educational ContextsPera et al. (2019): With a Little Help from My Friends: User of Recommendations at SchoolCharisi et al. (2022): Artificial Intelligence and the Rights of the Child: Towards an Integrated Agenda for Research and PolicyGómez et al. (2021): Evaluating recommender systems with and for children: towards a multi-perspective frameworkNg et al. (2018): Recommending social-interactive games for adults with autism spectrum disorders (ASD)General Links:
Follow me on LinkedInFollow me on TwitterSend me your comments, questions and suggestions to marcel@recsperts.comRecsperts Website

In episode 17 of Recsperts, we meet Miguel Fierro who is a Principal Data Science Manager at Microsoft and holds a PhD in robotics. We talk about the Microsoft recommenders repository with over 15k stars on GitHub and discuss the impact of LLMs on RecSys. Miguel also shares his view of the T-shaped data scientist.
In our interview, Miguel shares how he transitioned from robotics into personalization as well as how the Microsoft recommenders repository started. We learn more about the three key components: examples, library, and tests. With more than 900 tests and more than 30 different algorithms, this library demonstrates a huge effort of open-source contribution and maintenance. We hear more about the principles that made this effort possible and successful. Therefore, Miguels also shares the reasoning behind evidence-based design to put the users of microsoft-recommenders and their expectations first. We also discuss the impact that recent LLM-related innovations have on RecSys.
At the end of the episode, Miguel explains the T-shaped data professional as an advice to stay competitive and build a champion data team. We conclude with some remarks regarding the adoption and ethical challenges recommender systems pose and which need further attention.
Enjoy this enriching episode of RECSPERTS - Recommender Systems Experts.Don't forget to follow the podcast and please leave a review

(00:00) - Episode Overview
(03:34) - Introduction Miguel Fierro
(16:19) - Microsoft Recommenders Repository
(30:04) - Structure of MS Recommenders
(34:16) - Contributors to MS Recommenders
(37:10) - Scalability of MS Recommenders
(39:32) - Impact of LLMs on RecSys
(48:26) - T-shaped Data Professionals
(53:29) - Further RecSys Challenges
(59:28) - Closing Remarks
Links from the Episode:Miguel Fierro on LinkedInMiguel Fierro on TwitterMiguel's WebsiteMicrosoft RecommendersMcKinsey (2013): How retailers can keep up with consumersFortune (2012): Amazon's recommendation secretRecSys 2021 Keynote by Max Welling: Graph Neural Networks for Knowledge Representation and RecommendationPapers:
Geng et al. (2022): Recommendation as Language Processing (RLP): A Unified Pretrain, Personalized Prompt & Predict Paradigm (P5)General Links:
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