This document discusses different types of network experiments and interventions. It describes (1) using roommate assignments to make social connections exogenous, assessing peer effects on outcomes like GPA. It also discusses (2) natural experiments that manipulate exposure over existing networks, like popularity or voter turnout. Finally, it outlines (3) different types of network interventions, including targeting influential individuals, segmenting groups, inducing new connections, and altering network structure. The conclusion is that evidence from these experiments shows peer influence is real and we can now focus on how to leverage networks most effectively.

1. Network Experiments & Interventions

2. 1) Assessing Peer Effects
1) Manipulate networks to force connectivity to be exogenous
1) Roommate studies
2) Natural Experiments
2) Manipulate exposure over existing networks
1) Popularity
2) Voter Turnout
2) Interventions: Use networks to affect change
1) Valente’s 4 elements of network intervention
2) Exemplars
3) Network interference in “standard” experiments
4) What we’re ignoring: small group stuff
1) network exchange experiments
2) Transmission evolution experiments

3. Network Experiments & Interventions
Intro
Shalizi & Thomas: PI is *generally* confounded
General fear of confounding by unobserved selection features has pushed interest in
network experiments. How to make a social relation exogenous?

4. Network Experiments & Interventions
Problem

5. Network Experiments & Interventions
Problem

6. Network Experiments & Interventions
Problem

8. Roommates assigned randomly
within gender, & self-reported
smoking, study-style & messiness.
No evidence of pair-similarity
based on this sorting (i.e. all
evidence suggests randomness is
real)
Network Experiments & Interventions
Exogenous networks (W)

9. Assume that one’s one GPA
is a function of own ability
& peer ability and GPA
Network Experiments & Interventions
Exogenous networks (W)

10. Assume that one’s one GPA
is a function of own ability
& peer ability and
GPA…results suggest a
positive effect.
Similar effects on social
outcomes (joining a
fraternity, etc.)…
Network Experiments & Interventions
Exogenous networks (W)

11. Network Experiments & Interventions
Exogenous networks (W)

12. Network Experiments & Interventions
Exogenous networks (W)

13. Network Experiments & Interventions
Exogenous networks (W)

14. Note follow-up work (by Salganik & Watts) suggests the effects are weak and not long lasting
Network Experiments & Interventions
Exogenous networks (W)

16. Network Experiments & Interventions
Exogenous networks (W)
Control
treatment

17. Network Experiments & Interventions
Exogenous networks (W)

18. Network Experiments & Interventions
Exogenous networks (W)
SEPTEMBER 2010 VOL 329 SCIENCE

19. Network Experiments & Interventions
Exogenous networks (W)

20. Network Experiments & Interventions
Exogenous networks (W): Issues with experimental assignment
Sharique Hassan

21. Network Experiments & Interventions
Exogenous networks (W): Issues with experimental assignment
Sharique Hassan

22. Network Experiments & Interventions
Exogenous networks (W): Issues with experimental assignment
Sharique Hassan

23. Network Experiments & Interventions
Exogenous networks (W): Issues with experimental assignment
Sharique Hassan

24. Network Experiments & Interventions
Exogenous networks (W): Issues with experimental assignment
Sharique Hassan

25. Network Experiments & Interventions
Exogenous networks (W): Issues with experimental assignment
Sharique Hassan

26. Network Experiments & Interventions
Exogenous networks (W): Issues with experimental assignment
Sharique Hassan

27. Network Experiments & Interventions
Exogenous Behavior (Y)
4 types of interventions:
1) Individuals
1) Finding opinion leaders or flow blocking
nodes that play a key role in the network
process.  usually some centrality score, or an
adaptive algorithm. Here highlighted
“keyplayer” nodes.
2) Segmentation
3) Induction
4) Alteration

28. Network Experiments & Interventions
Exogenous Behavior (Y)
4 types of interventions:
1) Individuals
2) Segmentation
1) Use communities to break the groups into
parts, treat some use others as controls.
3) Induction
4) Alteration

29. Network Experiments & Interventions
Exogenous Behavior (Y)
4 types of interventions:
1) Individuals
2) Segmentation
3) Induction
1) Enhance relations & communication
4) Alteration

30. Network Experiments & Interventions
Exogenous Behavior (Y)
4 types of interventions:
1) Individuals
2) Segmentation
3) Induction
4) Alteration
1) Programs that seek to change the shape of the
network, add/remove ties or nodes

31. Network Experiments & Interventions
Exogenous Behavior (Y)

32. Network Experiments & Interventions
Exogenous Behavior (Y)
Exploit the “Friendship Paradox” idea…

33. Network Experiments & Interventions
conclusion
Many examples of network peer effects driven by experiments.
Many examples of how manipulations can change the network
itself
I think there’s sufficient evidence to start pushing harder against
the skeptics: peer influence is clearly real; question is now how do
we leverage it most effectively?