cross-community influence in discussion fora

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Digital Enterprise Research Institute www.deri.ie

Cross-Community Influence in Discussion Fora

Václav Belák, Samantha Lam, Conor Hayes

[email protected] http://www.StefanDecker.org/


Motivation

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forum A forum B

•  Online social communities represent an important cultural and business asset in context of many services on the Web

•  Management and exploitation of these communities has thus become important and one way to do it is to focus on influential actors

•  Social influence has been intensively studied in SNA, but can we extend the notion of influence to the level of communities?


Research Questions

•  How can we identify communities persistently affecting other communities?

•  Given a specific community, which communities does it influence? Which communities are dependent on the activity of others?

•  Over time, how can we identify that a community is being increasingly influenced or even overtaken by another community?


Methods: Definition of Impact

•  We propose to take two factors into account: 1.  degree of community membership of the users 2.  centrality of the users within each community

•  we used in-degree (# replies of a user) •  For general case of n users and k communities define:

•  n × k membership matrix M •  n × k centrality matrix C

•  Cross-community k × k impact matrix J can then be obtained as a product of the two matrices:

•  Communities have usually different sizes, we therefore work with normalised impact matrix:

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Methods: Impact-based Measures

•  Diagonal elements of J contain independence values (self-impact) •  Total impact a community has on others is its importance •  Total impact other communities have on a community is the community’s dependence •  Level of dispersion (heterogeneity) of importance/dependence of

community i can be measured as an entropy of a an i-th row/column of the impact matrix

•  Is a community broadly influential or does it influence only few other communities?

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Evaluation Data-Set

•  10 years of data of the largest Irish discussion board system •  Segmented using 1 week sliding window

•  1 week window represents approx. 84% of cross-fora posting activity

•  448 snapshots in total •  636 communities, 73k users, 8M posts


Clustering Fora By I. and D.

Aggregate impact matrices from the individual snapshots and cluster the communities (by k-means) embedded in the row and column spaces of the aggregate matrix.

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Jagg = J1 + J2

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Overall I/D over Time

Take the communities with the highest importance and dependence at each week and plot them over time.

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Soccer

Politics

IrelandOffline

Help Desk

Counter−Strike

Humour

Humanities

Computers & Tech.

Half−Life

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PBANKnights of the R.T.Spell CzechsEventsThe Cuckoo's NestLubnipAsk Doctor DementoHoLLThe ThunderdomeTipp InstFNWAIThe IlluminatiDigital Art & DesignHistory & HeritagePearTree HouseLord of the RingsComeonbanusModeratorsFreemasonsNewbies & FAQFeedbackScienceHelp DeskReaverTelevisionHumourRecycle BinHumanitiesWebgamesWork & JobsLiteratureAfter HoursSportsComputers & Tech.GamesFilmsRole Playing

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Cross-Community Infl. over Time

Count cases when community i’s impact on j was higher than j’s independence and plot the pairs with the highest counts.

Count From (i) To (j)

29 Moderators Reported Posts

22 FNWAI Poker

17 The Thunderdome After Hours

14 PI Mods Personal Issues


Moderation of Pers. Issues

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PI ModsModeratorsindependence


Conclusion

•  The evaluation demonstrated that the framework •  is able to identify highly influential and dependent communities •  can be used for efficient monitoring of the cross-community

activity, perhaps even for early alerts •  can identify which communities to stimulate (e.g. by posting a

message) s.t. the stimulus spreads efficiently •  We aim to extend it with content analysis

•  E.g. What are the most influential communities with respect to a particular topic?

•  We will also investigate empirically-observed topic cascades and modify our models accordingly if needed

•  Finally, our goal is to propose a method for measuring significance of cross-community impact

•  Belák V., Lam S., Hayes C. Cross-Community Influence in Discussion Fora. ICWSM 2012.

•  Belák V., Lam S., Hayes C. Targeting Communities to Maximise Information Diffusion. MSND/WWW 2012.


Fold, No, Wait, All In!

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