***** To join INSNA, visit http://www.insna.org ***** Hello everybody, I use a formula from Newman/Girvan (Phys. Rev. E 69 (2004) 026113) to calculate Q=SUMi(eii-ai*ai) with ai=SUMj(eij) from the k x k symmetric matrix e. eii is the fraction of links within the cluster k and ai is the row (or column) sum. Very easy to implement in standard statistical packages. Here are my questions: 1. Why has matrix e to be symmetric? 2. Why can ai*ai be characterized as an appropriate null model? (Both are questions from a reviewer ;-)) Best regards to the specialists Per _____________ Dr. Per Kropp Institute for Employment Research Regional Research Network Frau-von-Selmnitz-Str. 6, D-06110 Halle Germany Phone: +49/345-1332-236 (secretary: -255; fax: -555) mail: [log in to unmask] www.iab.de/iab-sachsen-anhalt-thueringen _____________________________________________________________________ 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.