Learning Whom to Trust with MACE
Written for the Research library (claude-opus-5-5) from the paper text, in our own words: the license "CC BY-NC-SA 3.0 (ACL Anthology, before 2016)" does not allow redistributing the text itself. Original — aclanthology.org/N13-1132.pdf
Summary
Crowdsourcing platforms such as Amazon's Mechanical Turk (AMT) make it cheap to collect categorical labels for NLP. However, some workers answer carelessly or strategically to earn money quickly, for example by always choosing the same option. Majority voting can be misled by such spammers. The authors propose MACE (Multi-Annotator Competence Estimation), an unsupervised item-response model. It treats true labels as hidden variables and gives each annotator a trustworthiness parameter plus a separate label distribution used only when that person is spamming. When not spamming, an annotator is assumed to give the correct label. The model is trained with EM or with Variational Bayes using sparse priors. They evaluate it on AMT datasets from Snow et al. (2008) and on synthetic adversarial data. MACE beats majority voting, matches more complex state-of-the-art systems, and estimates annotator reliability far better than agreement-based measures. Confidence thresholding and a few gold control items raise accuracy further. This matters because it allows cleaner corpora to be built cheaply from noisy crowd labels and helps identify which workers to rehire or block.
Key points
- Data: three discrete-label tasks from Snow et al. (2008):
- WSD: 177 items, 34 annotators.
- RTE: 800 items, 164 annotators.
- Temporal: 462 items, 76 annotators.
- Synthetic sets: 100 items with 2 or 4 labels, 20 simulated annotators, 10 answers per item.
- Training setup:
- EM runs 50 iterations with 100 random restarts and light smoothing of the M-step.
- The VB variant uses a symmetric Beta(0.5, 0.5) prior on trustworthiness and a Dirichlet prior fixed at 10.0 on spamming strategies.
- Annotator reliability: MACE-VB's trust estimates correlate with true annotator proficiency at Pearson ρ ≈ 0.90–0.91 on all three datasets. Raw agreement reaches 0.73–0.81, and Cohen's κ falls as low as 0.13 on WSD.
- Extra accuracy gains:
- Keeping only low posterior-entropy predictions trades coverage for higher accuracy.
- Supplying gold labels for some items as token constraints helps, and MACE exploits small amounts of supervision more effectively than the baseline.
- Release: MACE is a freely downloadable Java implementation from ISI. Its accuracy is comparable to the more complex model of Raykar and Yu (2012).
Cited by
- Zero-Shot Stance Detection: A Dataset and Model using Generalized Topic Representations
- We Need to Consider Disagreement in Evaluation
- Annotation Error Detection: Analyzing the Past and Present for a More Coherent Future
- Ranking Generated Summaries by Correctness: An Interesting but Challenging Application for Natural Language Inference
- A Crowdsourced Corpus of Multiple Judgments and Disagreement on Anaphoric Interpretation
- Two Contrasting Data Annotation Paradigms for Subjective NLP Tasks
Cite
@inproceedings{hovy2013learning,
title = {{Learning Whom to Trust with MACE}},
author = {Hovy, Dirk and Berg-Kirkpatrick, Taylor and Vaswani, Ashish and Hovy, Eduard},
booktitle = {Proceedings of the 2013 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies},
year = {2013},
url = {https://aclanthology.org/N13-1132/}
}References
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