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.
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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
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.
Northern Research Station
USDA Forest Service
Associate Research Scientist
Yale School of Forestry and Environmental Studies
New Haven, CT
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51 Mill Pond Road, Hamden CT 06514
Robert T. Trotter, II Ph.D.
Regents’ Professor and Chair
Department of Anthropology
575 East Pine Knoll Drive
Northern Arizona University
Flagstaff, AZ 86011
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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_____________________________________________________________________ SOCNET is a service of INSNA, the professional association for social network researchers (http://www.insna.org). To unsubscribe, send an email message to [log in to unmask] containing the line UNSUBSCRIBE SOCNET in the body of the message.