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Dr. Kets:
I don't know that any one definition exists that will make all critics
happy.  I attempted to use network exposure to measure peer effects
which was quite simply a calculation of the percentage of one's peers,
defined as those whom a person nominated in response to several network
questions (who do you turn to for advice, who do you consider friends,
etc.) who engage in a particular behavior (using contraceptive methods,
using hybrid seed corn, prescribing tetracycline, smoking, etc.).  Then
this definition is expanded to include the influence of ties of ties and
more distal social relations; and expanded to include other ways of
conceiving peers such as those who are structurally equivalent (also
varying the radius of social influence).
It is generally assumed that the greater number or proportion of peers
who engage in a behavior, the more likely one is to do so, but some
evidence exist that people have varying thresholds in their
susceptibility to peer effects.  These varying thresholds indicate that
some people will engage in behaviors when few others do, while other
people wait until a majority of their network engages in a behavior
before they are willing to do so.  There is also some evidence that peer
effects are affected by strength of tie, stronger ties have stronger
peer effects, for some behaviors (particularly risky ones).  For more
delightful reading on these results and related findings:

Valente, T. W. (In press). Models and methods for innovation diffusion.
In P. J. Carrington, J. Scott, & S. Wasserman (Eds.) Models and Methods
in Social Network Analysis. Cambridge, UK: Cambridge University Press.

Valente, T. W., Mouttapa, M. & Gallaher, M. (2004). Social network
analysis for understanding substance abuse: A transdisciplinary
perspective.  Substance Use & Misuse, 39, 1685-1712.

 Valente, T. W. (1995). Network models of the diffusion of innovations.
Cresskill, NJ: Hampton Press.

- Tom

Drs.W.Kets wrote:

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>Dear all,
>I am an economist working on social networks and social preferences. I'm afraid that sociological concepts are sometimes misused in the economics literature, as economists are a bit sloppy with the definitions. To avoid this pitfall, I'm looking for a good definition of "peer effects". Can anyone help me, perhaps?
>Willemien Kets
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To learn more about my evaluation book go to:
My personal webpage:
Thomas W. Valente, PhD
Director, Master of Public Health Program
Department of  Preventive Medicine
School of Medicine
University of Southern California
1000 S. Fremont Ave.
Building A Room 5133
Alhambra CA 91803
phone: (626) 457-6678
fax: (626) 457-6699
email: [log in to unmask]

SOCNET is a service of INSNA, the professional association for social
network researchers ( To unsubscribe, send
an email message to [log in to unmask] containing the line
UNSUBSCRIBE SOCNET in the body of the message.