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Generalized Venn and Venn-Abers Calibration with Applications in Conformal Prediction
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Extends Venn and Venn-Abers calibration from binary classification to generic loss functions, adds Venn multicalibration, and applies it to conformal quantile prediction with quantile-conditional coverage.
Problem
Point calibrators (histogram binning, isotonic regression) only guarantee calibration asymptotically and can be unreliable in finite samples; existing Venn/Venn-Abers calibration is limited to binary classification and regression, and lacks finite-sample multicalibration for generic losses.
Approach
Wraps any in-sample calibrated point calibrator in a Venn procedure: for each candidate imputed outcome, recalibrate on the augmented calibration set and collect the resulting predictions at the test context into a set guaranteed (marginally, finite-sample) to contain a perfectly calibrated prediction; applies this to generic losses via isotonic regression (Venn-Abers), offset-loss multicalibratio
Key results
- Venn-Abers conformal quantile intervals achieve ~0.90 marginal coverage on all six datasets and the lowest CCE on five of six (e.g., Bike 0.019 vs CQR 0.031, Concrete 0.035 vs 0.037 for CQR, Community 0.028 vs 0.031).
- Venn-Abers intervals are wider than CQR on several datasets (e.g., Concrete width 17 vs 16, Community 0.40 vs 0.38), reflecting the cost of finite-sample set calibration.
- Oracle Venn-calibrated mean predictions reduce multicalibration error versus point-calibrated predictions on all six datasets, e.g., Community 0.0055 vs 0.0209 and Star 0.0078 vs 0.0113.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use Venn-Abers quantile calibration instead of CQR | XGBoost-based conformal intervals · Bike, Bio, Star, Meps, Concrete, Community | conditional calibration error (CCE): 0.031 -> 0.019; 0.020 -> 0.017; 0.026 -> 0.024; 0.020 -> 0.018; 0.037 -> 0.035; 0.031 -> 0.028 | Helped |
| Use Venn-Abers instead of CQR | XGBoost-based conformal intervals · Bike, Bio, Star, Meps, Concrete, Community | marginal coverage: 0.90 vs 0.90 on all six datasets | No clear effect |
| Use Venn-Abers instead of CQR | XGBoost-based conformal intervals · Bike, Bio, Star, Meps, Concrete, Community | average interval width: 83 vs 98; 12 vs 14; 620 vs 780; 2.4 vs 2.7; 9.4 vs 16; 0.22 vs 0.38 (uncalibrated vs CQR); Venn-Abers: 100, 14, 780, 2.8 | Mixed |
| Use Venn multicalibration (oracle) instead of point-calibrated offset regression | XGBoost median regression · Bike, Bio, Star, Meps, Concrete, Community | multicalibration error: 0.0015 vs 0.0015; 0.0100 -> 0.0094; 0.0113 -> 0.0078; 0.0017 -> 0.0016; 0.0081 -> 0.0064; 0.0209 -> 0.0055 | Mixed |
| Use Venn multicalibration (oracle) instead of the uncalibrated model | XGBoost median regression · Bike, Bio, Star, Meps, Concrete, Community | multicalibration error: 0.0019 -> 0.0015; 0.0073 -> 0.0094; 0.0098 -> 0.0078; 0.0032 -> 0.0016; 0.0077 -> 0.0064; 0.0099 -> 0.0055 | Mixed |
Surprising findings
- Uncalibrated intervals miss the 90% target badly on some datasets (e.g., 0.71 coverage on Concrete), while the Venn-based methods are calibrated.
- The Venn-calibrated oracle mean prediction is worse than the uncalibrated model on Bio (0.0094 vs 0.0073), an exception to its general improvement.
Limitations
- Venn set calibration must be run separately for each test context, and for continuous outcomes requires discretizing the outcome space, which is approximate.
- Finite-sample guarantees are marginal; conditional calibration holds only asymptotically, with rates O_p(n^{-2/3}) for Venn-Abers and O_p(k(n)log(n/k(n))/n) for binning.
- Quantile-loss results need the conformity scores to be almost surely distinct from calibrated predictions; the weaker lower-bound case is not pursued.
Experimental setup
Datasets: MEPS Concrete Community STAR Bike Bio
Benchmarks: MEPS Concrete Community STAR Bike Bio
Metrics: marginal coverage conditional calibration error (CCE) average interval width multicalibration error prediction set width
Baselines: Uncalibrated CQR Marginal CP VM (Mondrian Venn) Calibrated (offset linear regression)
Builds on: Venn-Abers calibration Venn calibration conformalized quantile regression multicalibrated conformal prediction Mondrian conformal prediction
Closest papers by meaning
- Self-Calibrating Conformal Prediction (NeurIPS 2024 · similarity 0.94)
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- Co-optimization for Adaptive Conformal Prediction (NeurIPS 2026 · similarity 0.86)
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