1. Link creation and profile alignment in the aNobii social network Luca Maria Aiello Giancarlo Ruffo Rossano Schifanella Keywords : link creation, homophily, social influence, aNobii 2 nd IEEE International Conference on Social Computing Speaker: Luca Maria Aiello, PhD student aiello@di.unito.it Alain Barrat Ciro Cattuto Authors: Università degli Studi di Torino ISI Foundation

2. Open questions in social network analysis 1. What are the dynamics leading to link creation? 2. What is the interplay between user similarity and link creation? 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino2

3. 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino3 Dataset Static analysis Geographic analysis Dynamical analysis Conclusions Outline

4. 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino4 Dataset Static analysis Geographic analysis Dynamical analysis Conclusions Outline

5. Social network for bookworms Data-driven analysis on anobii.com 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino5 Social network ◦ Directed ◦ Friendship + neighborhood Profile features ◦ Library and wishlist ◦ Groups ◦ Tags 4 th snapshotFriendshipNeighborhoodUnion Nodes74,90854,59086,800 Links268,655429,482697,910 6 snapshots, 15 days apart Full giant connected component

6. 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino6 Dataset Static analysis Geographic analysis Dynamical analysis Conclusions Outline

7. Basic statistics 8.0 Reciprocation0.57 Avg SPL5.3 Diameter20 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino7 Broad distributions High reciprocation High diameter

8. Correlations and mixing patterns Pearson correlation k out ngng nbnb nwnw 10.310.18 ngng 10.320.31 nbnb 10.22 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino8 Positive correlations between: Connectivity and activity Different activities Assortativity (n.s.)

9. Profile similarity vs. social distance Topical overlap Statistical correlation because of assortative biases? Null model to discern real overlap from purely statistical effects ◦ No topical overlap other than that caused by statistical mixing patters 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino9 Does similarity between user profiles depend on the social distance?

10. 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino10 Dataset Static analysis Geographic analysis Dynamical analysis Conclusions Outline

11. Motivations …does geographical overlap hold in the network as well? Dataset peculiarities ◦ Many users specify their home country (97%) or town (38%) ◦ Particular community distribution 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino11

12. Geographical clustering 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino12 Country-level social network Zoom on Italy

13. Geographic and language overlap Null model test with random link rewire Country-level overlap due to language barriers City-level overlap for friendship (trivial…) City-level overlap for neighborhood ◦ Bidirectional causality connection between acquaintance in real life and connectivity in the online social network 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino13

14. 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino14 Dataset Static analysis Geographic analysis Dynamical analysis Conclusions Outline

15. Triadic closure Reciprocation is strong Users tend to choose “friends of their friends” as new friends 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino15 DirectReciprocated Bidirectional Closure Double closure 75%20% 25%30%10% Classification of new links at time t+1 between nodes already present at time t (t ∈ {1,…,5})

16. Proximity-driven attachment Users tend to choose “friends of their friends” or people close in the social network as new friends This process results in preferential attachment 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino16

17. Causality between similarity and link creation Topical overlap is observed for all profile features Three possible explanations: 1. Homophily (people connect with similar people) 2. Social influence (social connection conveys similarity) 3. Mixture of the two Explore the causality relationship between profile similarity and social linking 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino17 What is the cause of topical overlap?

18. Similarity  link creation 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino18 〈n cb 〉σbσb 〈n cg 〉σgσg d uv = 29.50.021.120.05 u → v 12.90.041.100.08 u ↔ v 18.50.041.670.11 Closure18.20.041.810.10 Dbl closure23.40.051.200.12 Average similarity of pairs forming new links between t 0 and t 0 +1 (t 0 =4), compared with average similarity of all the pairs at distance 2 at time t 0 Pairs that are going to get connected show a substantially higher similarity

19. Link creation  similarity 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino19 Evolution of the similarity between pairs linking together at different times Groups Books

20. 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino20 Dataset Static analysis Geographic analysis Dynamical analysis Conclusions Outline

21. Summary What are the dynamics that rule link creation? ◦ Reciprocation (in direct networks) ◦ Triadic closure ◦ Proximity-driven (preferential) attachment  On geographical space  On the social network ◦ Language-driven attachment ◦ Homophily What is the interplay between user similarity and link creation? ◦ Tight coupling (topical overlap) ◦ Topical overlap is caused by homophily and social influence both 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino21

22. Future work Link prediction Information spreading Extend analysis to other social systems 22/08/2010SocialCom 2010 - Luca Maria Aiello, Università degli Studi di Torino22

23. Speaker: Luca Maria Aiello aiello@di.unito.it www.di.unito.it/~aiello Thank you for your attention! 2 nd IEEE International Conference on Social Computing