In crowdsourcing, some tasks are conducted by the crowd due to enjoyment [8] or social reward [6]. However, arbitrary tasks are seldom enjoyable, and social award is often associated to some specific tasks, such as Wikipedia (https://en.wikipedia.org/wiki/Main_Page) and Stack Overflow (http://stackoverflow.com/). Thus, given an arbitrary task, a requester often needs to offer incentive (i.e., the cost of the task) to motivate workers to conduct the task. The cost per task is often paid in the form of financial compensation, a few cents per task. The quality of a crowdsourcing task is often referred as accuracy. Since the workers are humans, which may make errors when they perform tasks, the results returned by the crowd will have errors as a consequence. The trade-offs between cost and quality refer to the relationships between the financial incentive and the performance.

Wikip...