Crowdsourcing Blog Track Top News Judgments at TREC Richard McCreadie, Craig Macdonald, Iadh Ounis {richardm, craigm, 1

Outline Relevance Assessment and TREC (4 slides) Crowdsourcing Interface (4 slides) Research Questions and Results (6 slides) Conclusions and Best Practices (1 slide) 2

Relevance Assessment and TREC Slides 4-7/20 3

Relevance Assessment Relevance assessments are vital when evaluating information retrieval (IR) systems at TREC Is this document relevant to the information need expressed in the user query? Created by human assessors Specialist paid assessors, e.g. TREC assessors Typically, only one assessor per judgement (for cost reasons) Researchers themselves 4

Limitations Creating relevance assessments is costly $$$ Time Equipment (lab, computers, electricity, etc) May not scale well How many people are available to make assessments Can the work be done in parallel? 5

Task Could we do relevance assessment using crowdsourcing at TREC? TREC 2010 Blog Track Top news stories identification subtask “What are the newsworthy stories on day d for a category c?” Was the story ‘Sony Announces NGP’ an important story on the 1 st February for the Science/Technology category? 6 System Task: Crowdsourcing Task:

Crowdsourcing Interface Slides 9-12/20 7

Instructions... Crowdsourcing HIT Interface 8 Category c Day d Story Comment Box Submit button Judgment Assigned [+] Important [-] Not Important [x] Wrong Category [?] Not Yet Judged Externally Hosted iframe List of stories to be judged

External Interface Interface was hosted from our servers Requires Interaction Catches out bots which only look for simple input fields to fill 9 Glasgow Server Worker

Manual Summary Evaluation Hosting the judging interface externally allows us to record and reproduce what each worker sees Can see at a glance whether the judgments make sense Can compare across judgments easily Can check whether the work has been done at all 10 Worker 1/2/3 Is this a bot?

Submitting Larger HITs We have each worker judge 32 stories from a single day and category per HIT Two reasons: Newsworthiness is relative: Provides background for workers as to the stories of the day. Promotes worker commitment in the task Stories

Experimental Results Slides 14-20/20 12

Research Questions 1.Was crowdsourcing Blog Track judgments fast and cheap? 2.Are there high levels of agreement between assessors? 3.Is having redundant judgments even necessary? 4.If we use worker agreement to infer multiple grades of importance, how would this effect the final ranking of systems at TREC? 13 Was crowdsourcing a good idea? Can we do better?

Experimental Setup 14 $0.50 per HIT $ total (Includes 10% fees) US Worker Restriction 6 Batches Incremental improvements 8,000 news stories statMAP pooling depth topic days Three workers per HIT 24,000 judgments total 750 HITs total [O. Alonso, SIGIR’09]

Is Crowdsourcing Relevance Assessments Fast and Cheap? Quick? First HITs accepted within 10 minutes of launch Each batch took less than 5 hours Cheap? $ ($ per judgment) 38% above $2 per hour wage on average 15 Batches quickly completed – not an issue Few HITs per batch – might be difficult to find soon after launch Workers took less time than expected Workers get faster over time

Assessment Quality Are the assessments of good quality? Evaluate agreement between workers Mean Agreement – 69% Ellen Voorhees reported only 32.8% 16 [ E.M. Voorhees. IPM, 2000]

Do we need redundant judgments? What would have happened to the ranking of TREC systems if we had only used a single worker per HIT? Consider each of the three judgments per HIT from a Meta- Worker System rankings are not stable in the top ranks Do we need to average over three workers? 17 Two Groups: Top 3: ~0.15 apart Bottom 3: ~0.3 apart Multiple Ranking Swaps by the top systems Yes!

Conclusions and Best Practices Crowdsourcing top stories relevance assessments can be done successfully at TREC... But we need at least three assessors for each story Best Practices Don’t be afraid to use larger HITs If you have an existing interface integrate it with MTurk Gold Judgments are not the only validation method Re-cost your HITs as necessary 18 Questions?