Incentive Mechanism of
Crowd-Sourcing
Shangyu Xie
Supervised by Prof. Tian
Tap the power of Many to get things
DONE!
What is Crowdsourcing?
Crowdsourcing is the process of obtaining needed services, ideas or
content (Sourcing) by soliciting contributions from a large group of
people.(Crowd)
Easy!
No!
Ideality
Reality
Why?
Roughness of Data
Complexity of Human
Drive of Research
High-quality of Data
Cost-efficiency of Plan
Incentive Mechanism
We need encourage! It
is candy and ice-cream.
RULE is necessary!
Force &Encourage
How can it be possible?
What I have been doing
• Model it from a transaction view based on game theory
• Categorize and Estimate basic mechanisms which are commonly used
in application
• Try to set up a incentive mechanism work better
A Quick Introduction
Worker
Requester
Profit
r(q): reward function;
c(q): cost function;
High
Low
p-r(q),r(q)-c(1) -r(q),r(q)-c(0)
p: profit for the requester;
q: quality of workers’ work.
Free-riding
Validation approach
• Majority voting
• Standard testing
Two commonly used mechanisms
• Reward for consensus mechanism
• Reward for quality mechanism
Math(1)
Cost function c(q), q∈[0,1]
• Convex in q; c’(q) >0;
• c(q) differentiable in q;
• c(0)>0.
Utility function u(q), q∈[0,1]
• Convex in q;
• Made by worker.
Reward function r( )
• Undefined
• Why?
• Made by requester.
• Should be r(q), q∈[0,1]?
Math(2)
For consensus mechanism, let
• q be the one worker action;
• q’ be other workers’ action for task;
𝐾
𝐾!
Convergence probability p=
𝑞′𝑛 1 − 𝑞′ 𝐾−𝑛 ;
𝑛!(𝐾−𝑛)!
𝑛=𝐾 2
Where,
• K is the number of workers.
Further
• The utility the worker get u(q, q’)= 𝑟𝑞 • 𝑝(𝑞′) − 𝑐(𝑞);
Math(3)
• The final utility of worker should be
Further,
𝑢(𝑞, 𝑞′ = 1) = 𝑟𝑞 − 𝑐(𝑞 );
𝜕𝑢(𝑞, 1)
|𝑞=1 = 𝑟 − 𝑐′(1) ≥ 0
𝜕𝑞
So what does it mean?
Budget (at least)
𝐵 = (𝐾 + 1)𝑟 ≥ (𝐾 + 1)𝑐′(1)
Math(4)
For accuracy mechanism, let
• e be the validation costs for work;
• α be the percent of validated; ∈(0,1]
Then, the expected utility
𝑢 = 𝑟[(1 − 𝛼) + 𝛼𝑞] − 𝑐(𝑞 );
Following the same,
𝜕𝑢
|
= 𝑟𝛼 − 𝑐′(1) ≥ 0
𝜕𝑞 𝑞=1
𝑐′(1)
𝑟≥
𝛼
Math(5)
• Finally, the budget is
𝐵 = (1 − 𝛼)𝑟 + 𝛼𝑑
𝑐′(1)
=(1 − 𝛼)
+ 𝛼𝑑
𝛼
𝑐′(1)
=
+ 𝛼𝑑 + 𝑐′(1);
𝛼
My Thought
Tricky but worth a try.
What’s next?
• Combine the two to find a best trade-off
• More tricky,
focus on r( ), also can be controlled by requester!
Thanks a lot for listening!
Q&A!