Outline Social Contagion Social Contagion Social Contagion Social - PowerPoint PPT Presentation

Social Contagion Outline Social Contagion Social Contagion Social Contagion Social Contagion Models Models Principles of Complex Systems Background Background Granovetter’s model Granovetter’s model Course 300, Fall, 2008 Network version Network version Groups Groups Social Contagion Models Chaos Chaos Background References References Prof. Peter Dodds Granovetter’s model Network version Department of Mathematics & Statistics Groups University of Vermont Chaos References Licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License . Frame 1/86 Frame 2/86 Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Models Models Background Background Granovetter’s model Granovetter’s model Network version Network version Groups Groups Chaos Chaos References References Frame 4/86 Frame 5/86

Social Contagion Social Contagion Framingham heart study: Social Contagion Social Contagion Social Contagion Models Models Examples abound Background Background Granovetter’s model Granovetter’s model Network version Network version ◮ fashion Groups Groups ◮ Harry Potter Chaos Chaos ◮ striking References References ◮ voting Evolving network stories: ◮ smoking ( ⊞ ) [6] ◮ gossip ◮ The spread of quitting smoking ( ⊞ ) [6] ◮ residential ◮ Rubik’s cube segregation [15] ◮ The spread of spreading ( ⊞ ) [5] ◮ religious beliefs ◮ ipods ◮ leaving lectures ◮ obesity ( ⊞ ) [5] SIR and SIRS contagion possible ◮ Classes of behavior versus specific behavior: dieting Frame 6/86 Frame 7/86 Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Models Models Background Background Granovetter’s model Granovetter’s model Network version Network version We need to understand influence Groups Groups Chaos Chaos ◮ Who influences whom? Very hard to measure... References References Two focuses for us ◮ What kinds of influence response functions are ◮ Widespread media influence there? ◮ Word-of-mouth influence ◮ Are some individuals super influencers? Highly popularized by Gladwell [8] as ‘connectors’ ◮ The infectious idea of opinion leaders (Katz and Lazarsfeld) [12] Frame 8/86 Frame 9/86

The hypodermic model of influence Social Contagion The two step model of influence [12] Social Contagion Social Contagion Social Contagion Models Models Background Background Granovetter’s model Granovetter’s model Network version Network version Groups Groups Chaos Chaos References References Frame 10/86 Frame 11/86 The general model of influence Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Models Models Background Background Why do things spread? Granovetter’s model Granovetter’s model Network version Network version Groups Groups ◮ Because of system level properties? Chaos Chaos References References ◮ Or properties of special individuals? ◮ Is the match that lights the fire important? ◮ Yes. But only because we are narrative-making machines... ◮ We like to think things happened for reasons... ◮ System/group properties harder to understand ◮ Always good to examine what is said before and after the fact... Frame 12/86 Frame 13/86

The Mona Lisa Social Contagion The completely unpredicted fall of Eastern Social Contagion Europe Social Contagion Social Contagion Models Models Background Background Granovetter’s model Granovetter’s model Network version Network version Groups Groups Chaos Chaos References References ◮ “Becoming Mona Lisa: The Making of a Global Icon”—David Sassoon ◮ Not the world’s greatest painting from the start... Timur Kuran: [13, 14] “Now Out of Never: The Element of Frame 14/86 Frame 15/86 ◮ Escalation through theft, vandalism, parody, ... Surprise in the East European Revolution of 1989” The dismal predictive powers of editors... Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Models Models Background Background Granovetter’s model Granovetter’s model Network version Network version Groups Groups Chaos Chaos Messing with social connections References References ◮ Ads based on message content (e.g., Google and email) ◮ Buzz media ◮ Facebook’s advertising: Beacon ( ⊞ ) Frame 16/86 Frame 17/86

Getting others to do things for you Social Contagion Examples Social Contagion Social Contagion Social Contagion Models Models Background Background A very good book: ‘Influence’ by Robert Cialdini [7] Granovetter’s model Granovetter’s model Network version Network version ◮ Reciprocation: Free samples, Hare Krishnas Groups Groups Six modes of influence Chaos Chaos ◮ Commitment and Consistency: Hazing References References 1. Reciprocation: The Old Give and Take... and Take ◮ Social Proof: Catherine Genovese, Jonestown 2. Commitment and Consistency: Hobgoblins of the ◮ Liking: Separation into groups is enough to cause Mind problems. 3. Social Proof: Truths Are Us ◮ Authority: Milgram’s obedience to authority 4. Liking: The Friendly Thief experiment. 5. Authority: Directed Deference ◮ Scarcity: Prohibition. 6. Scarcity: The Rule of the Few Frame 18/86 Frame 19/86 Getting others to do things for you Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Models Models Background Background Granovetter’s model Granovetter’s model Network version Network version Groups Groups Chaos Chaos References References Other acts of influence ◮ Cialdini’s modes are heuristics that help up us get through life. ◮ Conspicuous Consumption (Veblen, 1912) ◮ Useful but can be leveraged... ◮ Conspicuous Destruction (Potlatch) Frame 20/86 Frame 21/86

Social Contagion Social Contagion Social contagion models Social Contagion Social Contagion Social Contagion Models Models Thresholds Background Background Granovetter’s model Granovetter’s model Some important models Network version Network version ◮ Basic idea: individuals adopt a behavior when a Groups Groups Chaos Chaos ◮ Tipping models—Schelling (1971) [15, 16, 17] certain fraction of others have adopted References References ◮ ‘Others’ may be everyone in a population, an ◮ Simulation on checker boards individual’s close friends, any reference group. ◮ Idea of thresholds ◮ Fun with Netlogo and Schelling’s model [20] ... ◮ Response can be probabilistic or deterministic. ◮ Threshold models—Granovetter (1978) [9] ◮ Individual thresholds can vary ◮ Herding models—Bikhchandani, Hirschleifer, Welch ◮ Assumption: order of others’ adoption does not (1992) [1, 2] matter... (unrealistic). ◮ Social learning theory, Informational cascades,... ◮ Assumption: level of influence per person is uniform (unrealistic). Frame 22/86 Frame 23/86 Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Social Contagion Models Models Some possible origins of thresholds: Background Background Granovetter’s model Granovetter’s model Network version Network version ◮ Desire to coordinate, to conform. Groups Groups Chaos Chaos Granovetter’s Threshold model—definitions ◮ Lack of information: impute the worth of a good or References References ◮ φ ∗ = threshold of an individual. behavior based on degree of adoption (social proof) ◮ Economics: Network effects or network externalities ◮ f ( φ ∗ ) = distribution of thresholds in a population. � φ ∗ ◮ Externalities = Effects on others not directly involved ∗ = 0 f ( φ ′ ∗ ) d φ ′ ◮ F ( φ ∗ ) = cumulative distribution = ∗ φ ′ in a transaction ◮ φ t = fraction of people ‘rioting’ at time step t . ◮ Examples: telephones, fax machine, Facebook, operating systems ◮ An individual’s utility increases with the adoption level among peers and the population in general Frame 24/86 Frame 26/86