When Average Calibration Fails: Site-Conditional Federated Conformal Risk Control
Conformal risk control (CRC) provides distribution-free segmentation guarantees by calibrating a prediction-set threshold on held-out data. In federated deployments, the standard approach pools calibration scores into a single threshold. We quantify, on real multi-institutional brain tumor data (FeTS-2022, 1,251 subjects, 20 institutions), a critical failure: naive pooled CRC protects the average hospital but violates coverage at 40% of individual institutions, with the worst site exceeding the target false-negative rate by 7.8 percentage points. We trace this failure to a hidden design choice: the aggregation weights implicitly determine whose coverage is protected. Sample-size weighting...
| Authors | Nafis Fuad Shahid |
|---|---|
| Primary category | cs.LG |
| Published | 18 June 2026 |
| Last updated at source | 24 July 2026 |
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