This paper tests whether the social information provided by the internet affects the decision to participate in politics. In a field experiment, subjects could choose to sign petitions and donate money to support causes. Participants were randomized into treatment groups that received varying information about how many other people had participated and a control group receiving no social information. Results show that social information has a varying effect according to the numbers provided, which is strongest when there are more than a million other participants, supporting claims about critical mass, and tipping points in political participation.
Read more: Margetts, H., John, P., Escher, T. and Reissfelder, S. (2011) Social Information and Political Participation on the Internet: an Experiment. European Political Science Review 3: 321-344.