Reeves, N., West, P. and Simperl, E. (2018) “"A Game Without Competition Is Hardly a Game": The Impact of Competitions on Player Activity in a Human Computation Game"”, Proceedings of the AAAI Conference on Human Computation and Crowdsourcing, 6(1), pp. 154-163. doi: 10.1609/hcomp.v6i1.13329.