Exploring iterative and parallel human computation processes

Services like Amazon's Mechanical Turk have opened the door for exploration of processes that outsource computation to humans. These human computation processes hold tremendous potential to solve a variety of problems in novel and interesting ways. However, we are only just beginning to understand how to design such processes. This paper explores two basic approaches: one where workers work alone in parallel and one where workers iteratively build on each other's work. We present a series of experiments exploring tradeoffs between each approach in several problem domains: writing, brainstorming, and transcription. In each of our experiments, iteration increases the average quality of responses. The increase is statistically significant in writing and brainstorming. However, in brainstorming and transcription, it is not clear that iteration is the best overall approach, in part because both of these tasks benefit from a high variability of responses, which is more prevalent in the parallel process. Also, poor guesses in the transcription task can lead subsequent workers astray.