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Dear Emese, dear all,
If you have data on personal networks, you may have information that can be used to account for shared companions outside the personal network, e.g., shared social settings, whether two alters are colleagues/family etc - usually of ego. That could be an important control variable (with ergms with personal networks). If you are intrinsically interested in the effect of shared companions, it still wonīt do - as David said. But if it is a control variable (which I suppose it typically is in personal networks) and if you interpret the effects with the type of data in mind, I think itīs okay - in the absence of statistical models that are better suited for understanding the structure of egonetworks at a relationship level.
Ramon y Cajal Researcher
Laboratory for Personal Networks and Communities (egolab-GRAFO)
Department of Social and Cultural Anthropology
Autonomous University of Barcelona
----- Original Message -----
From: David Lockhart <[log in to unmask]>
Date: Monday, February 20, 2012 9:51 pm
Subject: Re: [SOCNET] Ego Networks & ERGM
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> Emese -
> It can be appropriate to use ERGMs to model a complete network
> based on
> statistics observed in ego networks, however I think that looking
> at shared
> partner effects is problematic in such a context. Gwdsp is based
> on the
> number of dyads with exactly k shared partners, but the ego
> networks are
> not going to have the same pattern here as the complete network.
> There are
> two reasons for this.
> One is that the ego networks give a downwardly biased estimate of the
> number of shared partners of two alters, that is we don't know how
> manyshared partners they have where the shared partner does not
> have a tie to
> ego and therefore does not appear in the ego network.
> The other is that the sampling design ensures that all alters will
> have at
> least one shared partner (ego). Unless the degree distribution of
> egos is
> very small, most dyads are alter-alter pairs. This will tend to
> upwardlybias the number of dyads that have 1 or more shared partner.
> Together, that means you have a measure that is biased, but it
> isn't clear
> which direction the bias is in, so you can't even regard your
> estimate as a
> minimum or maximum.
> That may just mean you want to take gwdsp out of your model and
> fit a
> different ERGM. Possibly there is some other way of measuring
> structure you could use that would be less problematic. Triangles
> have a
> much more natural fit to ego network data than shared partners, for
> example. If dyadwise shared partners is something that you are truly
> interested in here, that is problematic and I don't think that a
> solution would be helpful, as the problems arise from the nature
> of the
> data and are not specific to ERGMs.
> On Mon, Feb 20, 2012 at 8:52 AM, Emese Domahidi <[log in to unmask]
> > ***** To join INSNA, visit http://www.insna.org *****
> > Dear all,
> > I am computing ERGM Models for ego networks of approximately 90
> egos and
> > their alteri. The ego networks are not interconnected. I
> constructed an
> > overall model for all networks, controlling for different network
> > structures (e.g. edges and gwdsp) and different individual and
> dyadic> attributes. The model is converging and the model fit is ok.
> > My question is whether constructing an overall model instead of
> looking at
> > each ego network individually is an appropriate way to model
> ERGM for
> > ego networks. I would really appreciate comments on this
> approach as well
> > as
> > literature recommendations on ego networks and ERG models.
> > Cheers, Emese
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