Online labor markets such as oDesk, Amazon Mechanical Turk, and TaskRabbit have been growing in importance over the last few years. In these markets, employers post tasks on which remote contractors work and deliver the product of their work. As in most online marketplaces, reputation mechanisms play a very important role in facilitating transactions, since they instill trust and are often predictive of the future satisfaction of the employer. However, labor markets are usually highly heterogeneous in terms of available task categories; in such scenarios, past performance may not be a representative signal of future performance. To account for this heterogeneity, in our work, we build models that predict the performance of a worker based on prior, category-specific feedback. Our models assume that each worker has a category-specific quality, which is latent and not directly observable; what is observable, though, is the set of feedback ratings of the worker and of other contractors with similar work histories. Based on this information, we build a multi-level, hierarchical scheme that deals effectively with the data sparseness, which is inherent in many cases of interest (i.e., contractors with relatively brief work histories). We evaluate our models on a large corpus of real transactional data from oDesk, an online labor market with hundreds of millions of dollars in transaction volume. Our results show an improved accuracy of up to 47% compared to the existing baseline.
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