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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 many
shared 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 upwardly
bias 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 higher-order
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 non-ERGM
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]>wrote:

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>
> 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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