Efficiently learning the accuracy of labeling sources for selective sampling

Many scalable data mining tasks rely on active learning to provide the most useful accurately labeled instances. However, what if there are multiple labeling sources ('oracles' or 'experts') with different but unknown reliabilities? With the recent advent of inexpensive and scalable online annotation tools, such as Amazon's Mechanical Turk, the labeling process has become more vulnerable to noise - and without prior knowledge of the accuracy of each individual labeler. This paper addresses exactly such a challenge: how to jointly learn the accuracy of labeling sources and obtain the most informative labels for the active learning task at hand minimizing total labeling effort. More specifically, we present IEThresh (Interval Estimate Threshold) as a strategy to intelligently select the expert(s) with the highest estimated labeling accuracy. IEThresh estimates a confidence interval for the reliability of each expert and filters out the one(s) whose estimated upper-bound confidence interval is below a threshold - which jointly optimizes expected accuracy (mean) and need to better estimate the expert's accuracy (variance). Our framework is flexible enough to work with a wide range of different noise levels and outperforms baselines such as asking all available experts and random expert selection. In particular, IEThresh achieves a given level of accuracy with less than half the queries issued by all-experts labeling and less than a third the queries required by random expert selection on datasets such as the UCI mushroom one. The results show that our method naturally balances exploration and exploitation as it gains knowledge of which experts to rely upon, and selects them with increasing frequency.