***** To join INSNA, visit http://www.insna.org ***** Dear Kim and social networkers, p* and p2 do not contain each other either way. p* has an in principle unlimited possibility for network effects (and p2 doesn't); the practical limitation resides in the estimability of these effects (cf. Snijders, Pattison, Robins, Handcock, New specifications for exponential random graph models; To be published, Sociological Methodology; downloadable from http://stat.gamma.rug.nl/sprh_f.pdf p* now is often referred to as ergm (exponential random graph model). On the other hand, p2 has random effects for representing between-actor differences (and p* doesn't). However, in/out/mixed-twostars effects in p* have to some degree a similar functionality; but the interpretability of unexplained variances at the actor level, which is a feature of p2, is not available in p*. The focus of p2 is on testing effects of covariates, which can be actor-bound or dyad-bound, and which can interact with reciprocity; while controlling for differential actor tendencies to sending and receiving ties, and for reciprocity. The focus of p*/ergm is on structurally modeling networks (which may include covariate effects). For p2, better estimation methods have been an advantage; recently there have been advances in estimation methods for both p*/ergm and p2, and p*/ergm now is in much better shape than with the earlier pseudolikelihood methods. I think that with recent and almost finished work on multivariate and multilevel p2, p2 retains an advantage concerning availability of good estimation methods across a range of model extensions. (The new January 2006 release of Stocnet will contain a new p2 version with multivariate and multilevel options.) p*/ergm has the advantage of a much better representation of structural network effects. Best regards, Tom Kim Se Kwon wrote: > ---------------------- Information from the mail header ----------------------- > Sender: Social Networks Discussion Forum <[log in to unmask]> > Poster: Kim Se Kwon <[log in to unmask]> > Subject: Does p* contain p2? > ------------------------------------------------------------------------------- > > ***** To join INSNA, visit http://www.insna.org ***** > > I've read some papers about p* and one paper about p2. > > If I've read correctly, Equation 4 of reference 2 ;extends ;first p* > (equation 1) to contain covariates. And p2 is 'the extension of p1 that > doesn't assume dyadic independence and accounts for nodal & dyadic > covariates.' > > Does p* (equation 4 in reference 2) contain p2? Because p* has p1 as > submodels, p2's model equation is very similar to p*'s. If not, what is the > unique features of p2? > > Thanks in advance for any comments. > > --- Equations --- > Equation 1 of Reference 2 ; : ; P(X = x) ;= exp(theta' * ;t(x)) / c(theta) > Equation 4 of Reference 2 ; : ; P(X = x) = exp(vec(x)' Z beta + sum of > alpha_k * d_k(x) + theta' * t(x)) / c(alpha, beta, theta) ; (d_k : the > number of individuals with exactly k links, Z : exogenous dyadic > covariates) > > > --- References --- > 1. Logit models and logistic regressions for social networks : I An > Introduction to markov graphs and p*. Stanley ;Wasserman... > 2. statnet: An R package for the Statistical Analysis and Simulation of > Social Networks, Mark S. Handcock... > 3. p2: a random effects model with covariates for directed graphs. Marijtje > A. J. van Duijn... > > > Best Regards > Se Kwon, Kim > > ------------- > KAIST (Korean Advanced Institute of Science & Technology) > Mathematics Student > http://math.kaist.ac.kr > > _____________________________________________________________________ > 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. -- Tom A.B. Snijders Professor of Statistics and Methodology Scientific Director, ICS Department of Sociology, University of Groningen Grote Rozenstraat 31 9712 TG Groningen The Netherlands +31-(0)50-3636188/6216 http://stat.gamma.rug.nl/snijders/ Note: new email address: [log in to unmask] _____________________________________________________________________ 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.