[statnet_help] Interpreting attribute-based geometrically weighted effects in two-mode networks

[Steffen Triebel]

Dear all,

I hope you had enjoyable holidays.

 

I’m currently working on a large two-mode network (500 events, 9500 actors). My current specification includes mostly effects such as nodematch or b2star in combination with attributes and gives theoretically meaningful results. I initially thought that the fit (both upon visual inspection and based on p-values) was no reason for concern, but upon closer inspection it seems that the MCMC diagnostics point to model degeneracy.

 

As far as I can tell the trace and density plots are all fine. The Geweke-diagnostics are all far from zero on all individual sample statistics but the auto-correlation, while constantly decreasing, takes quite a while to get close to zero (my understanding is that any statistic after lag 0 should be close to zero). To improve this, I tried adding geometrically weighted effects (gwb1degree, gwb1dsp, ..). It seems that no matter what combination of effects I try here (effects, decay and cutoff), I can’t get the models to converge. My guess is that this is because the network is highly formalized and not as organic as a school class for example. Now, I tried substituting the attribute-based b2star-effects with gwb2degree(attr=”covar_name”, decay=0.5, fixed=T) and these work fine, which is good. However, I am at a loss on how to interpret this, as each gwb2degree-effect produces two significant parameters (the attributes are dummy covariates, so one for each value) with basically the same parameter estimate. The estimated parameters are also very large.

 

In sum, I have four questions:
Are the MCMC-diagnostics as described here actually a reason for concern?
 
How do I interpret the parameters that gwb2degree produces?
 
Anything else I can do to improve my model? My controls currently are: (MCMLE.maxit=200, MCMC.burnin=3000, MCMC.interval=5000, MCMC.samplesize=10000)
 
How can I specify the constraint that actors have a minimum degree of 1 and events have a maximum degree of 40? This should also help with further estimations, I hope.
 

Cheers & enjoy the rest of the year,

Steffen

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