COMP 621U WEEK 3 SOCIAL INFLUENCE AND NFORMAT|○ND|FFUS|ON Nathan Liu (nliu(@cse. Ust. hk)
COMP 621U WEEK 3 SOCIAL INFLUENCE AND INFORMATION DIFFUSION Nathan Liu (nliu@cse.ust.hk)
What are social Influences 口| nfluence: a People make decisions sequentially a Actions of earlier people affect that of later people a two class of rational reasons for influence: a Direct benefit: Phone becomes more Useful if more people use it a Informational: Choosing restaurants a Influences are the results of rational inferences from limited information
What are Social Influences? Influence: People make decisions sequentially Actions of earlier people affect that of later people Two class of rational reasons for influence: Direct benefit: ◼ Phone becomes more useful if more people use it Informational: ◼ Choosing restaurants Influences are the results of rational inferences from limited information. 2
Herding: Simple Experiment Consider an urn with 3 ball. It can be either: a Majority-blue: 2 blue 1 red a Majority-red: 2 red, 1 blue n Each person wants to best guess whether the urn is majority is majority-blue or majority-red n Experiment: One by one each person a Draws a ball a Privately looks at its color ad puts it back a Publicly announces his quess o Everyone see all the guesses beforehand 口 How should you guess?
Herding: Simple Experiment Consider an urn with 3 ball. It can be either: Majority-blue: 2 blue 1 red Majority-red: 2 red, 1 blue Each person wants to best guess whether the urn is majority is majority-blue or majority-red: Experiment: One by one each person: Draws a ball Privately looks at its color ad puts it back Publicly announces his guess Everyone see all the guesses beforehand How should you guess? 3
Herding: What happens 口 What happens? a is person: guess the color drawn a 2nd person: guess the color drawn person: If the two before made different guesses then go with his own color Else: just go with their guess(regardless of the color you see o Can be modeled Bayesian rule( the first two guesses may bias the prior) a P(RIrrb)=P(rrb R)P(R)/P(rrb)=2/3 口 Non-optimal outcome: a With prob 1/3x1 3=1 /9, the first two would see the wrong color from then on the whole population would guess wrong
Herding: What happens? What happens? 1 st person: guess the color drawn 2 nd person: guess the color drawn 3 rd person: ◼ If the two before made different guesses, then go with his own color ◼ Else: just go with their guess (regardless of the color you see) Can be modeled Bayesian rule(the first two guesses may bias the prior) P(R|rrb)=P(rrb|R)P(R)/P(rrb)=2/3 Non-optimal outcome: With prob 1/3×1/3=1/9, the first two would see the wrong color, from then on the whole population would guess wrong 4
Examples: Information Diffusion 5 obscure technology ry tech blog Slashdot high-profile blog Wired New Scientist SJ Merc New York BBC Times
Examples: Information Diffusion 5