While many popular casual games use three-star systems, which give players up to three stars based on their performance in a level, this technique has seen limited application in human computation games (HCGs). This gives rise to the question of what impact, if any, a three-star system will have on the behavior of players in HCGs. In this work, we examined the impact of a three-star system implemented in the protein folding HCG Foldit. We compared the basic game's introductory levels with two versions using a three-star system, where players were rewarded with more stars for completing levels in fewer moves. In one version, players could continue playing levels for as many moves as they liked, and in the other, players were forced to reset the level if they used more moves than required to achieve at least one star on the level. We observed that the three-star system encouraged players to use fewer moves, take more time per move, and replay completed levels more often. We did not observe an impact on retention. This indicates that three-star systems may be useful for re-enforcing concepts introduced by HCG levels, or as a flexible means to encourage desired behaviors.
Keywords: analytics; design; games; human computation.