[Rsiena-help] Effects of covariate similarity on the evolution of a bipartite graph?

[Matteo Gagliolo]

Dear RSiena users,

	I'm trying to analyze a two-mode network representing
interlocking directorates. I have covariates for the mode 
corresponding to boards, and I would like to see if there is 
a tendency of directors to join boards with similar covariates
(or equivalently, a tendency of boards to form interlocks with 
similar boards). Sort of an homophily at distance 2.

Taking the boards as mode one, I think this effect could be 
implemented as an interaction among egoX and altDist2,
as the latter would represent the average X of boards on which
a certain director is already sitting.

Here comes my problem: altDist2 is currently "blacklisted" in the 
code for bipartite nets. Diving into the code (RSienaTest r. 220)
I found out where it all happens: in file effects.r:773, function 
covarBipartiteEff (comments are mine, to explain the issue):
---
covarBipartiteEff<- function(covarname, poszvar, moreThan2, nodesetNbr,
                                 name)
    {
        covRateEffects  <-  NULL
        if (nodesetNbr == 1) 
        {#This is the branch taken as the covariate is on the 1st mode(boards)
            covObjEffects <-
                createEffects("covarBipartiteObjective", covarname,
                              name=varname,
                              groupName=groupName, group=group,
                              netType=netType) #This returns "altX"  "altSqX"    
"egoX"    "altDist2" "simDist2", each replicated as eval/creat/endow
            covObjEffects <-
                covObjEffects[covObjEffects$shortName %in%
                              c("egoX"), ] #Here only "egoX" effects are 
selected
 ---          

So, it seems the code is currently allowing only for egoX effects for
covariates of the 1st mode.

Does anyone have an idea why? As all distance 2 nodes are in the same mode, I 
don't see why altDist2 and simDist2 should be blacklisted. 

Or maybe there is a more correct way to implement the "distance 2 
homophily" I am interested in?

Thanks,

Matteo

-- 
Matteo Gagliolo <mgagliol at ulb.ac.be>
Group for research on Ethnic Relations, Migration and Equality (GERME),
Institute of Sociology;
Machine Learning Group (MLG), Computer Science Department.
Université Libre de Bruxelles (ULB).
GERME, ULB, CP 124, 44 av. Jeanne
1050 Brussels, Belgium
Phone +32 2 650 4798, Fax +32 2 650 4659
http://homepages.ulb.ac.be/~mgagliol/