An Extensive Empirical Study on Semi-supervised Learning
Bibliographic record
Abstract
Semi-supervised classification methods utilize unlabeled data to help learn better classifiers, when only a small amount of labeled data is available. Many semi-supervised learning methods have been proposed in the past decade. However, some questions have not been well answered, e.g., whether semi-supervised learning methods outperform base classifiers learned only from the labeled data, when different base classifiers are used, whether selecting unlabeled data with efforts is superior to random selection, and how the quality of the learned classifier changes at each iteration of learning process. This paper conducts an extensive empirical study on the performance of several commonly used semi-supervised learning methods when different Bayesian classifiers (NB, NBTree, TAN, HGC, HNB, and DNB) are used as the base classifier, respectively. Results on Transductive SVM and a graph-based semi-supervised learning method LLGC are also studied for comparison. The experimental results on 26 UCI datasets and 6 widely used benchmark datasets show that these semi-supervised learning methods generally do not obtain better performance than classifiers learned only from the labeled data. Moreover, for standard self-training and co-training, when selecting the most confident unlabeled instances during learning process, the performance is not necessarily better than that of random selection of unlabeled instances. We especially discovered interesting outcomes when drawing learning curves for using NB in self-training on some UCI datasets. The accuracy of the learned classifier on the testing set may fluctuate or decrease as more unlabeled instances are used. Also on the mushroom dataset, even when all the selected unlabeled instances are correctly labeled in each iteration, the accuracy on the testing set still goes down.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.040 | 0.133 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.002 |
| Bibliometrics | 0.005 | 0.006 |
| Science and technology studies | 0.002 | 0.004 |
| Scholarly communication | 0.003 | 0.007 |
| Open science | 0.003 | 0.002 |
| Research integrity | 0.002 | 0.003 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".