Why Voluntary Contributions? Google Answers!

We study the pricing and tipping behaviour of users of the online service 'Google Answers'. While they set a price for the answer to their question ex ante, they can additionally give a tip to the researcher ex post. We develop a model that is based on reciprocal theories of social preferences pioneered by Rabin (1993) and extended by Dufwenberg and Kirchsteiger (2004). The predictions of our model are empirically tested with the field data we obtained. In line with the related experimental literature we conclude that an open contracts design encourages people to tip. This is motivated by reciprocity when people are socially-minded, but also by strategic considerations to build up a good reputation. Moreover, researchers seem to adjust their effort based on the user's previous tipping behaviour. Higher effort levels are reached when a sufficient tip history is available and efficiency is increased