POMDP-based control of workflows for crowdsourcing

Crowdsourcing, outsourcing of tasks to a crowd of unknown people ("workers") in an open call, is rapidly rising in popularity. It is already being heavily used by numerous employers ("requesters") for solving a wide variety of tasks, such as audio transcription, content screening, and labeling training data for machine learning. However, quality control of such tasks continues to be a key challenge because of the high variability in worker quality. In this paper we show the value of decision-theoretic techniques for the problem of optimizing workflows used in crowdsourcing. In particular, we design Al agents that use Bayesian network learning and inference in combination with Partially-Observable Markov Decision Processes (POMDPs) for obtaining excellent cost-quality tradeoffs. We use these techniques for three distinct crowdsourcing scenarios: (1) control of voting to answer a binary-choice question, (2) control of an iterative improvement workflow, and (3) control of switching between alternate workflows for a task. In each scenario, we design a Bayes net model that relates worker competency, task difficulty and worker response quality. We also design a POMDP for each task, whose solution provides the dynamic control policy. We demonstrate the usefulness of our models and agents in live experiments on Amazon Mechanical Turk. We consistently achieve superior quality results than non-adaptive controllers, while incurring equal or less cost. (C) 2013 Elsevier B.V. All rights reserved.