1. Scale Free and Small Worlds Networks: Studying A-Synchronous Discussion Groups Gilad Ravid Open University of Israel & Haifa University gilad@ravid.org

2. Asynchronous discussion groups as Small World and Scale Free Networks by Gilad Ravid and Sheizaf Rafaeli September Issue first pick September Issue first pick http://www.firstmonday.org/issues/issu e9_9/ravid/index.html http://www.firstmonday.org/issues/issu e9_9/ravid/index.html

4. Social Network Analysis

5. SNA  Network analysis is the study of social relations among a set of actors. It is a field of study -- a set of phenomena or data which we seek to understand

6. Small World Networks  Two characteristics A small average path length A small average path length Mean shortest node-to-node pathMean shortest node-to-node path A large clustering coefficient A large clustering coefficient How many of a node’s neighbors are connected to each otherHow many of a node’s neighbors are connected to each other

7. Scale Free Networks  Scale-free networks are characterized by a power-law distribution of a node’s degree.

9. Some Published Networks ( adapted from Newman 2003 ) CαlZmn 0.782.33.48113.43 25,516,48 2 449,913U film actors film actors 0.34-4.614.4455,3927,673U company directors company directors 0.56-7.573.92496,489253,339U math coauthorship math coauthorship 0.16 1.5/2.0 4.951.4486,30059,912D Email messages 3.22,810U sexual contacts sexual contacts 0.08 1.3/1.4 4.630,6358,830D Discussion Groups 0.442.770.13 17,000,00 0 460,902U Word co- occurrence Word co- occurrence info 0.392.53.315.9831,99210,697U Internet tech 0.08-18.992.676,5944,941U power grid power grid 0.28-3.977.682,359307D Neural networks Neural networks bio social

10. Kevin Bacon http://oracleofbacon.org/oracle/ Shoshi Marciano Sassi Keshet Jason Patric Kevin Bacon Nisuim Nusah Tel Aviv, 1979 The Beast of War,1988 Sleepers, 1996

12. Neural network of C. Elegans

13. Syphilis Transmission in Georgia

14. Corporate Partnerships

15. Internet Connections (CAIDA)

16. Linking language lexicon

17. Power Transmission Grid of Western US

19. Small World Networks Affects  CPL -> Information percolation / Speed of Diffusion  Cliquishness  Personal problems Find jobs Find jobs Find information / answers Find information / answers  Group problems Disasters recovery Disasters recovery Inventions Inventions  Group decision making  Hard to forecast network dynamics

21. Scale-Free Networks  …. are common  … important category in networks study  Have very connected members (Hubs)  Hubs have a key role  ….results of self organized network  … growth with preferential attachment mechanism

22. Scale Free Networks Affects  Continuous hierarchy of members  No characterized member  Resistance to failure  Sensitivity to attacks  We know how they form  Information diffusion  Rich get richer

23. Research Sample  Discussion groups of more than 400 courses  Courses taught 1999-2002  158,276 messages

24. Why discussion groups?  The main carriage for cooperative learning and working  Knowledge management  Sage on the Stage to Guide on the Side  Shared memory (space)  Equal opportunity to read and write messages  Message are the links between participants and knowledge  One can read (lurk) other discussions

25. Research populations Percentage of Number The Population A100%75,409 All Registered Participants A A16.5%12,506 Participants who sent at least 1 message B B28.8%3,609 Non active Participants (received no answers and did not answer others) C B0.5%67 Participants who only answered themselves D B70.6%8,830 Regular Participants E

26. Sig. RR2R2 b1b1 b0b0 Model 0.0000.812-1.3125647.469Output Degree 0.0000.929-1.93725389.80Input Degree 0.0000.826-1.47731915.51All Degree

29. CCCPL 0.0854.66618Discussion Groups Network 0.0007.3625Random Network (Average encompassing three networks) 0.00039287.3045Theoretical Random Network 2160.63Ratio between random network and discussion groups

30. Creation of a scale-free net  Growth and preferential attachment

31. Scale-Free Networks: Mechanisms 1. Growth 2. Preferential Attachment

33. Gilad Ravid gilad@ravid.org http://www.ravid.org/gilad gilad@ravid.org http://www.ravid.org/giladThanksQuestionsAnswers