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Bob
You can take a diffusion perspective in which:
1) All of the nodes are used to construct an adjacency matrix.  This can 
be initially created by making a link list of all the counties that are 
next to one another and converting this to an adjacency matrix in UCINET 
or any one of the other commonly used tools.
2) Then construct a matrix vector of the initially invasive species.  
You may have multiple such vectors if studying different species across 
the same terrains.
3) Then it is a simple process of matrix multiplication to construct the 
network exposure terms over time and convert this to an event history 
framework and determine if exposure is associated with infestation.

I wrote all of this in GAUSS such that the input is the link list or 
node list and a vector indicating time at infestation.  The time vector 
gets converted to an over-time adoption matrix and carries out the 
matrix multiplication to get exposure terms.  It also calculates 
infectiousness and susceptibility (per Strang and Tuma, 1993; Myers, 
2000).  It will also calcuate thresholds to adoption, how much exposure 
required for an infestation to occur.  It is summarized in my diffusion 
chapter.

 

We are have converted much of this to STATA/MATA which we can share and 
my next task is to learn R and run it in that environment.


-Tom

Robert Talbot Trotter II wrote:

> ***** To join INSNA, visit http://www.insna.org *****
>
> Please see the request below, which I am forwarding from my son. He is 
> a Forest Service research ecologist who is also moving into areas that 
> will include human, as well as invasive species,  network analysis.  
> He is in the process of becoming a member of INSA, but also has grant 
> and data analysis deadlines to meet.  Please feel free to copy him on 
> any responses, and I will copy him on any general responses to the 
> list serve.  Thanks. Bob Trotter
>
>  
>
> _______________________________________________________________________________________
>
> FORWARDED MESSAGE
>
> Greetings!  I'm hoping members of the SOCNET listserve might be able 
> to send me in the right direction, as I am new to network analyses. 
>  My research is focused on identifying and evaluating patterns of 
> spread for invasive species (mostly insects) across the landscape, a 
> process that is essentially a spatially based network study. 
>  Currently, I am attempting to do something that is probably quite 
> simple, but being new to the network software available, I'm hoping to 
> get some suggestions for the best software to use for the following 
> data parameters.
>
> Essentially, I would like to determine the pattern of spread between 
> nodes (which in this case are centroids in counties in the eastern 
> U.S.), using the following assumptions.
>
> 1) The first node (county) with the invasive species is known.
> 2) The species can move to new nodes (counties), only if the counties 
> share a physical border, I have a nodelist/adjacency matrix with this 
> information.
> 3) A new node (county) is infested following the infestation of a 
> neighboring node (county).
> 4) If two neighbors are infested at the same time, the source of 
> infestation will be the closest county centroid, such that nodes 
> (counties) are only infested by a single source.
>
> Which network programs would you recommend to create an appropriate 
> data set to analyze, and to visualize, this process.
>
>  
>
> If there are software packages out there that can animate this 
> process, that would be even better.  Many thanks!
>
> R Talbot Trotter III, Ph.D.
> Research Ecologist
> Northern Research Station
> USDA Forest Service
>
> Associate Research Scientist
> Yale School of Forestry and Environmental Studies
> New Haven, CT
>
> Phone: 203-432-3978
> Mobile: 928-380-6812
> Fax: 203-230-4315
> [log in to unmask] <mailto:[log in to unmask]>
> 51 Mill Pond Road, Hamden CT 06514
>
>  
>
> ------------------------------------------------------------------------------------------------------------------------------------------
>
> Robert T. Trotter, II Ph.D.
>
> Regents' Professor and Chair
>
> Department of Anthropology
>
> Room 101G
>
> 575 East Pine Knoll Drive
>
> Northern Arizona University
>
> Flagstaff, AZ 86011
>
> Email: [log in to unmask] <mailto:[log in to unmask]>
>
> Phone: 928-523-4521
>
> Mobile: 928-380-8684
>
> Fax: 928-523-9135
>
>  
>
> _____________________________________________________________________ 
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-- 
Thomas W. Valente, PhD
Director, Master of Public Health Program
http://www.usc.edu/medicine/mph/
Department of  Preventive Medicine
Keck  School of Medicine
University of Southern California
1000 S. Fremont Ave., Unit #8
Building A Room 5110		
Alhambra CA 91803		
phone: (626) 457-4139
cell: (626) 429-4123
fax: (626) 457-6699
email: [log in to unmask]

My personal webpage:
http://www-hsc.usc.edu/~tvalente/

The Empirical Networks Project
http://ipr1.hsc.usc.edu/networks/

Evaluating Health Promotion Programs
(Oxford U. Press):
www.oup-usa.org/isbn/0195141768.html


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