8 Neel Sundaresan What a Flake! CHICAGO - Two sisters from Virginia sold their Illinois-shaped corn flake on eBay Friday night for $1,350. "We were biting our nails all the way up to the finish, seeing what would happen," said Melissa McIntire, 23. "There's a lot of relief involved." The winner of the auction, which lasted more than a week, is the owner of a trivia Web site who wants to add the corn flake to a traveling museum. Illinois-shaped corn flake sells for $1,350 Winner of the eBay auction wants to add the flake to a traveling museum
9 Neel Sundaresan Heir to Some Hair! Hair Sold As Washington's Nets $17K Saturday, February 23, 2008 Four strands reportedly clipped from the first president were sold at auction Friday night to a Richmond man who declined to give his name. Colorado resident Christa Allen said her father, a Philadelphia attorney, had given her the hair, which was pressed under glass in a locket and accompanied by a watch.
10 Neel Sundaresan Scathing Limbaugh Letter Nets $2.1M By BRIAN SKOLOFF – Oct 19, 2007 WEST PALM BEACH, Fla. (AP) A letter from Democratic senators blasting conservative talk show host Rush Limbaugh for using the phrase "phony soldiers" on his program was sold Friday on eBay for a record $2.1 million.
11 Neel Sundaresan Up for auction is a composite of all 4 pages of the Harry Reid smear letter and all the signatures into one 8.5 X 31.5 scroll document. The image shown in the auction is cropped for legibility. The acutual document does contain all of the signatures. This will make a great conversation piece and will get the goat of any Rush hating liberal. Would look great in a custom frame or as a Scroll haning on the wall. My cost to print, post & mail is about $10.00. I have a couple more to auction even though I lost money on the 1st one. It is still worth it. PayPal or Money Order. Shipping to US/Canada is $3.00.
12 Neel Sundaresan A vehicle sells every 2 minutes A part or accessory sells every 3 seconds Diamond jewelry sells every 83 seconds A Timberland shoe sells every 10 minutes A trading card sells every 6 seconds On an average day on eBay… What wags the Tail? eBay users trade about $1,400 worth of goods on the site every second.
14 Neel Sundaresan The Long Tail Nature Buyers outnumber sellers 5:1 Seller-items sold has a power law distribution Seller-revenue has a power law distribution Buyer-items bought has a power law distribution For a sample period over 1 month mean is 3 and median is 1 Buyer-spent money has a power law distribution For a sample period of 1 month mean is 98$ and median was 45$ Categories browsed mean 10.5, median 5 ~10M new items a day, most items eventually sell, items last from a day to 30 days, most items not cataloged, some auction-some fixed price
17 Neel Sundaresan Pareto and the Long Tail Vast majority of products appeal to small number of users Vast majority of products of this nature can only be carried by small number of sellers These account for sizable consumption Selling less of more becomes important
18 Neel Sundaresan Britney Spears Jessica Simpson Jessica Alba Christina Aguilera Tara Reid Lindsey Lohan Rainbow Brite Rocket Dog Shoes Hair Photo Poster dolls Paris Hilton Perfume Parikh, Sundaresan
19 Neel Sundaresan Evolution of Jessica Simpson
23 Neel Sundaresan Long Tail and Diversity Diversity is important to avoid market collapse The Fractal Nature of the Long Tail helps Diversity Long Tail affords diversity through Mass Customization
24 Neel Sundaresan Lemon Markets and the Long Tail Sellers have better knowledge of the goods for sale; buyers dont Buyers have no way of verifying Seller is incentivised to pass of poor quality goods through sale as buyer has no way of verifying Creates market inefficiencies, guarantees are indefinites, and such markets disappear George Akerloff, The Market for Lemons: Quality Uncertainty and Market Mechanism (1970) Bad drives out the Good Greshams Law: Bad Money (Counterfeits) Drives Good Money out of Circulation
30 Neel Sundaresan Reputation Sharing of reputation lowers the ability of dishonest agent to profit in the future Dishonest agents will have to seek new partners – who will pay only discounted Lemon price : (Trust Discount) Dishonest agents can still trade outside the coalition boundaries Private Reputation vs Public (Shared) Reputation
31 Neel Sundaresan Reputation Sharing of reputation lowers the ability of dishonest agent to profit in the future Dishonest agents will have to seek new partners – who will pay only discounted Lemon price : (Trust Discount) Dishonest agents can still trade outside the coalition boundaries Private Reputation vs Public (Shared) Reputation
32 Neel Sundaresan Feedback and Networks: Auroral Diagrams Arts and Crafts Collectibles Global
33 Neel Sundaresan eBay Feedback History Before 1999 Anybody could leave feedback for anybody Now Feedbacks are per-transaction between seller and winning bidder Accumulative Positive (+1), Negative (-1), Neutral(0) 1 line of qualitative textual feedback Feedback Profile is public Any prospective buyer can see all per-transaction feedback with scores and text Feedback 2.0 Revealed on multiple aspects of the user feedback Today Only buyers can leave feedbacks, sellers can only leave positive feedbacks
34 Neel Sundaresan eBay Feedback Most Feedbacks are positive (Pollyanna effect) Negatives are fewer Fear of retaliation Satisfaction of receipt No Feedbacks instead Positive with text specifying negative experiences High courtesy Equilibrium (Resnick/Zeckhauser 01) Mutually negative feedbacks may represent misplaced blame Who goes first? Since buyer typically pays first, expect seller to go first Buyer goes first twice as often (Resnick/Zeckhauser 01)
36 Neel Sundaresan Analysis of Feedback Text (Sundaresan et al 2007)
37 Neel Sundaresan eBay Feedback – Rated Aspect Summary (Lu, Sundaresan, Zhang – 2009) Break down comments into head terms (aspects) and qualifiers (opinions) Phase 1: Identify k interesting aspects and cluster data into these – k-means / PLSA / Structured PLSA Use priors (Dirichlet) act as training to bias clustering results Then use MAP (Max. A Posteriori) to estimate all the parameters Phase 2: Identify rating functions for the k aspect clusters using local (per-user) or global rating information WWW09 – Lu, Sundaresan, Zhang, Rated Aspect Summarization / Thu DM- 5 (Opinions) 2:30-4pm
38 Neel Sundaresan Expression/Sentiment Expression is a metaphor for Trust When Trust is expressed through feedback or textual communication it influences mutual Trust and future Trust Factors to take into account What a user usually says What is the change in what the user usually says How does what someone says affects what the next user says Only those who have significantly significant things to say do say anything at all
39 Neel Sundaresan Do Sellers care about their feedback? Sellers can respond to a negative feedback The text of the response is displayed below the feedback text More than a third of the sellers respond to negative feedback Sound of Silence relates somewhat to fear of retaliatory feedback Other studies Behavioral changes after a negative feedback Improved behavior vs non-participation Retaliation
40 Neel Sundaresan Trust and Reputation Trust is subjective, Reputation is objective Trust is relative, Reputation is global Trust is personal, Reputation is collective A trusts B because B has a good reputation A trusts B in spite of not knowing Bs reputation A trusts B in spite of Bs bad reputation Reputation may change as Trust between agents change though Reputation measures cannot be oversensitive to trust changes
41 Neel Sundaresan Transparent vs Opaque Mechanisms Transparency helps understand and improve negative behavior Opaque is useful to verify mechanism and also evaluate actors and avoid gaming Both are important in a reputation system
42 Neel Sundaresan Enforcing Trust - Behavioral Economics Penalizing or Promoting in Ranking Coupons and Incentives (Un)Fortunately, When enforcements are opaque, strategies to learn the system Transparency can be useful but can be gamed
47 Neel Sundaresan A Flow Model for Reputation Good buyers buy from Trustworthy Sellers Trustworthy Sellers sell to Good buyers A mutually recursive equation leads to an equation of the form Initialize Reliability score s i (0), b i (0) assuming people are basically good!
48 Neel Sundaresan Reputation for Augmenting Features Reputation ranking makes reputation as integral part of relevance sort A Marketplace Search like eBay is complex Diverse items, Diverse sellers, Diverse scenarios Reputation has to be combined with relevance and other factors like diversity Reputation can used as a ranking function for any feature
49 Neel Sundaresan In Summary… People are basically good On theMedianAverage