Seminars at the Faculty of Informatics

You are cordially invited to attend the PhD Dissertation Defense of Giovanni Luca CIAMPAGLIA on Thursday, December 15th 2011 at 10h00 in room A33 (Red building)

This thesis explores the phenomenon of user participation in peer production communities. In large-scale collaboration communities such as wikis, open source software development teams, and file-sharing groups, members are, in general, not remunerated for contributing to the digital common, so the incentives to participate to these projects are usually construed in terms of extrinsic benefits such as reputation gains, reciprocity, gratification, and sense of membership to a socially cohesive group. In fact, like any social group, a community of commons-based peer production is endowed with its own norms, beliefs, and cultural features. In these systems such features, however, are themselves the result of a bottom-up process of cultural formation and opinion aggregation, mostly related to various aspects of the social production of digital contents.

Unfortunately it is still poorly understood how this process happens -- considering that most interactions between members are mediated by the digital artifacts (encyclopedic articles, source code, etc.) that the project is producing. To this end, we studied the process of community formation in a large peer production community by means of statistical analysis and agent-based modeling and simulation.

In the first part of this thesis we analyzed the activity of registered editors from the communities of five of the largest versions of Wikipedia, the free online encyclopedia. We found that the distribution of the user activity lifespan is distributed according to a mixture of log-normal distributions.

In order to understand these empirical patterns we developed, in the second part of the thesis, an agent-based model of a peer production community. Social influence is modeled in terms of dyadic user-page interactions, under the form of the bounded confidence rule. Thus a measurable aspect of user participation -- activity lifespan -- is linked to microscopic features of the dynamics of social influence. In order to study the behavior of our model, we perform a factor screening via global sensitivity analysis. We then calibrate our agent-based model using the empirical data from Wikipedia. To this end, an indirect inference technique is devised and tested.

In light of the results of our model, in the third -- and final -- part of the thesis we analyze a recent dataset from the English Wikipedia and perform a longitudinal study of the life cycle of user activity. Using a non-parametric approach we study how the daily rate of editing changes during the lifespan of editors, and find a strongly inhomogeneous temporal life cycle. This approach enables us to look at the temporal evolution of editing activity for the whole community of Wikipedia editors.

These results suggest that user participation to peer production systems can be construed primarily as a process of mediated social influence and that other factors, most surprisingly intrinsic motivation to contribution, are less important in determining the overall activity lifespan of an individual. In conclusion this thesis shows how social simulation can be supplemented with large-scale data analysis in order to develop an empirically grounded approach to the computational study of collective social phenomena and, in particular, social computing platforms.

Dissertation Committee:

  • Prof. Luca Maria Gambardella, UniversitÓ della Svizzera italiana, Switzerland (Research Advisor)
  • Prof. Fabio Crestani, UniversitÓ della Svizzera italiana, Switzerland (Internal Member)
  • Prof. Michele Parrinello, UniversitÓ della Svizzera italiana, Switzerland (Internal Member)
  • Dr. Santo Fortunato, Institute for Scientific Interchange, Italy (External Member)
  • Prof. Kristina Lerman, University of Southern California, United States (External Member)

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