Semi-Supervised Majority Voting for crowdsourcing

Crowdsourced datasets often suffer from missing labels, significantly degrading classifier performance. In this paper, we propose Semi-Supervised Majority Voting (SSMV), a novel framework that integrates semi-supervised learning into the aggregation process to mitigate these effects. First, SSMV partitions the crowdsourcing label matrix into a “sparse” region (with many missing entries) and a “dense” region (with mostly observed labels), yielding two complementary sample sets. Next, it jointly learns a reconstruction coefficient matrix — regularized by an ${\ell }_{2,1}$-norm to suppress noise and redundancy — by minimizing the discrepancy between the original and reconstructed label matrices. A graph-based Laplacian term preserves the intrinsic manifold structure during reconstruction, while a learned worker-selection vector filters out low-quality annotators. Finally, we apply classic majority voting to the refined label matrix to infer final labels. Extensive experiments on synthetic and real-world datasets demonstrate that SSMV consistently outperforms state-of-the-art crowdsourcing classifiers across multiple metrics. By explicitly modeling the relationship between missing-label patterns and overall label distributions, SSMV not only recovers missing labels more accurately but also enhances overall classification accuracy. This semi-supervised mechanism is readily extensible to other aggregation algorithms, providing a general strategy for enhancing crowdsourced label quality.