Mao, A. et al. 2013. Volunteering Versus Work for Pay: Incentives and Tradeoffs in Crowdsourcing. Proceedings of the AAAI Conference on Human Computation and Crowdsourcing. 1, 1 (Nov. 2013), 94–102. DOI:https://doi.org/10.1609/hcomp.v1i1.13075.