ac#ve&learning&and&crowd1 … · rewards&and&par#cipa#on&rates& •...
TRANSCRIPT
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Ac#ve Learning and Crowd-‐Sourcing for Machine Transla#on
Vamshi Amba#, Stephan Vogel, & Jamie Carbonell
Pramod Thammaiah
ScoC Brinker
November 17, 2010 CS 286r
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• Ac#ve Learning: a few labeled instances, a large set of unlabeled instances, and a ranking of instances for an external oracle to label them
• Ac#ve Crowd Transla#on: using crowd-‐sourced experts and non-‐experts to translate sentences as the external oracle
• Mechanical Turk: Amazon’s crowd-‐sourcing plaQorm where “requesters” post HITs (human intelligence tasks) for “turkers” to complete in exchange for micropayment rewards.
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• Qualifica#ons for turkers can include: – Sufficient accuracy on a small test set
– Minimum percentage of previously accepted submission
– Geographic loca#on (e.g., China for Chinese transla#on)
– Op#on to reject unsa#sfactory work
• Pricing for turkers varies, but generally inexpensive: – As low as as < $0.01 per transla#on
– Empirical study in paper averaged $0.015/transla#on
– Supply/demand factors for less common languages
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Density Weighted Diversity Sampling (DWDS) Strategy
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• Transla#on Reliability Es#ma#on as inter-‐annotator agreement
– Agreement of 3/3 translators 21.1% of the #me
– Agreement of 2/3 translators 23.8% of the #me
• Translator Reliability Es#ma#on as iden#fying reliable translators over a series of transla#ons
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• Catalog and data management
– Confirm accuracy of catalog data, iden#fy duplicates
– Select best images to showcase a catalog item
• Database crea#on – Content harves#ng
• Search op#miza#on & content management
– Tag content with keywords to improve searchability
– Ensure content adheres to certain guidelines
Mechanical Turk in Commercial Applica#ons
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• Other applica#ons?
• Ethical concerns?
Ques#ons About Crowdsourcing with Mechanical Turk
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Crowdsourcing and All-‐Pay Auc#ons
Pramod Thammaiah
ScoC Brinker
November 17, 2010 CS 286r
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Introduc#on
• Examines crowdsourcing in things like Tasken, Yahoo! Answers, etc.
• Want to understand the rela#onship between rewards and par#cipa#on rates
• Presents mathema#cal model and empirical analysis based off of All-‐pay auc#ons
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All Pay Auc#ons
• All-‐pay auc#ons are those where each agent pays their bid before alloca#on of the good
• The highest bidder wins the good
• Examples: poli#cal elec#ons, Swoopo, lobbying, bidding on the value of a wallet, etc.
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Basic Model
• Consider a 2-‐stage all-‐pay auc#on – Each player selects a contest and makes a bid (think of the bid as effort)
– For each contest, the player with the highest bid wins
• Each player has a private skill that is known only to them
• The reward of each contest and the distribu#on of skills is known to all players
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Mock contest
• Pick one of the 2 contests: – Write the best joke
– Write the best riddle
• The winner will be selected by Prof. Chen – So make them short….
• The best joke will get $1 and the best riddle will get $2
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Mathema#cal Formula#on
•
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Proposi#on 3.1: There exists a symmetric equilibrium
• Let be the probability that a player selects contest be the cumula#ve distribu#on over skill for a player given that he selects , and
• Let denote the expected profit of a player with skill for contest then using Revenue Equivalence we have:
• Note that this is not an unique equilibrium – Consider 2 players and 2 contests. Then player 1 always picking contest 1 and player 2
always picking contest 2 regardless of skill is an asymmetric equilibrium
• Corollary: Given a set of contests with the same reward. A player will only choose a contest in that he has the maximum skill.
• Assume that all players only choose symmetric strategies
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Large-‐System Limit
• The number of contests needs to stay propor#onal to the number of agents in the limit
• Assume that there are only, K, finitely many classes of rewards
• The number of par#cipants in each contest is a Poisson random variable, whose mean is logarithmic in the size of the reward
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Player-‐Specific skills
• Assume that every contest requires the same skill, or formally,
• In this case the symmetric equilibrium is unique.
• Let contests be grouped into K classes, based on having the same reward – Where and for nota#onal simplicity:
– For any subset we define:
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Theorem 4.1
• Under the player-‐specific skills, the symmetric equilibrium sa#sfies the following two proper#es:
1. Threshold Reward: A contest is selected by a player with strictly posi#ve probability only if the reward offered by this contest is one of the highest rewards, where
– Intui#on: At a certain point, contests with low rewards will get no par#cipants.
2. Par#cipa#on rates: A player selects a par#cular contest of class with probability given by
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Theorem 4.2
Players have a minimum reward level and compete in contests at or above this level with decreasing probability. The minimum reward level increases with skill level. Overall, contests with higher rewards get more players.
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Contest-‐Specific Skills
• A player’s skills for each contest are drawn independently
• A player will only need to pay aCen#on to his highest skill in each reward class
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Extensions
• Asymmetric Skills – Suppose the maximum skill m is specific to each contest class
– Can we infer these maximal skill levels by examining par#cipa#on levels? (ie. Make it endogenous)
• Minimum Effort – Corresponds to having a minimum bid, or entry fee
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System Design
• Maximize overall social welfare • There is u#lity gained with a greater number of par#cipants in a contest.
• There is a cost associated with the rewards that are paid
• In a zero-‐cost setng, op#mal rewards are unique up to a mul#plica#ve constant
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All-‐Pay Auc#ons Empirical Results (taskcn.com)
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• Tasks on the Chinese web site Taskcn
• Tasks with a single winner in the year 2008
• Graphics, Characters, and Miscellaneous categories
• Par#cular focus on Graphics category including: – Logos subcategory
– 2-‐D design subcategory
– Conjecture: these subcategories use homogeneous skills
Comparing Empirical Analysis to Analy#cal Predic#ons
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Heterogeneity of tasks? Sort of logarithmic
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1,431 tasks had 774 dis#nct winners—however, a group of 122 users accounted for 50% of all winning submissions
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Summary
• Players randomize dependent on the skill level they get
• Contests with rewards below a certain threshold get no par#cipants
• Players in certain intervals of skills have a certain interval of contests they par#cipate in – As skills increase, they only par#cipate in the highest paying contest
• Logarithmic rela#onship between rewards and par#cipa#on (in large systems)
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Further Ques#ons
• Why can players only pick one contest? – Not the case since 122 players won over 50% of 1431 contests
• What if we had mul#ple winners? • How can we capture the “#me-‐element” of these
situa#ons? • What if the market becomes so big that it becomes
difficult to search for tasks? • Why is there a drop-‐off in par#cipa#on for contests with
high rewards? • What may be other highly influen#al externali#es?
• Differences between money and reputa#on?
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