Crowdsourced top-k algorithms

Crowdsourced top-k computation has attracted significant attention recently, thanks to emerging crowdsourcing platforms, e.g., Amazon Mechanical Turk and CrowdFlower. Crowdsourced top-k algorithms ask the crowd to compare the objects and infer the top-k objects based on the crowdsourced comparison results. The crowd may return incorrect answers, but traditional top-k algorithms cannot tolerate the errors from the crowd. To address this problem, the database and machine-learning communities have independently studied the crowdsourced top-k problem. The database community proposes the heuristic-based solutions while the machine-learning community proposes the learningbased methods (e.g., maximum likelihood estimation). However, these two types of techniques have not been compared systematically under the same experimental framework. Thus it is rather difficult for a practitioner to decide which algorithm should be adopted. Furthermore, the experimental evaluation of existing studies has several weaknesses. Some methods assume the crowd returns high-quality results and some algorithms are only tested on simulated experiments. To alleviate these limitations, in this paper we present a comprehensive comparison of crowdsourced top-k algorithms. Using various synthetic and real datasets, we evaluate each algorithm in terms of result quality and efficiency on real crowdsourcing platforms. We reveal the characteristics of different techniques and provide guidelines on selecting appropriate algorithms for various scenarios.