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Learning Fair Policies for Multi-Stage Selection Problems from Observational Data
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Proposes a multi-stage fair selection framework that learns interpretable linear selection policies from biased observational data using inverse probability weighting and sample average approximation, reformulated as a mixed binary conic program.
Problem
Learning fair multi-stage selection policies (e.g., hiring, loan approval, bail) from observational data where outcomes are only observed for selected candidates, so training data suffers selection bias and fairness constraints must hold on the future population.
Approach
Combine IPW-based counterfactual evaluation of selection policies with sample average approximation of an infinite chance-constrained program over linear stage-wise selection rules, using an epsilon-conservative approximation that yields a mixed binary conic (MIP) reformulation solvable by off-the-shelf solvers.
Key results
- On the synthetic data, the proposed IPW-based model reaches 76.51% precision and 0.031 unfairness versus 68.57% precision and 0.050 unfairness for the existing selection policy at N=800.
- Across semi-synthetic real datasets, the Fair model reduces unfairness by roughly 17% to 55% relative to the No-Fair model (e.g., 37.5% on German, 35.71% on COMPAS) with small precision loss.
- Without IPW (No-IPW), the learned policies violate selection constraints in up to 60% of test trials at N=2000, while IPW violations drop to 0% at larger sizes.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| apply the Fair setting instead of No-Fair | ε-IPWMFS on Adult · Adult | precision: 0.52 ± 0.05 -> 0.51 ± 0.04 (1.92%) | Hurt |
| apply the Fair setting instead of No-Fair | ε-IPWMFS on Adult · Adult | unfairness: 0.26 ± 0.19 -> 0.17 ± 0.13 (34.61%) | Helped |
| apply the Fair setting instead of No-Fair | ε-IPWMFS on German · German | precision | Mixed |
| apply the Fair setting instead of No-Fair | ε-IPWMFS on German · German | unfairness | Helped |
| apply the Fair setting instead of No-Fair | ε-IPWMFS on COMPAS · COMPAS | precision: 0.67 ± 0.04 -> 0.60 ± 0.09 (10.45%) | Hurt |
| apply the Fair setting instead of No-Fair | ε-IPWMFS on COMPAS · COMPAS | unfairness: 0.14 ± 0.04 -> 0.09 ± 0.06 (35.71%) | Helped |
Surprising findings
- Without IPW, constraint violation ratios can remain high or even increase with training size (e.g., 60% at N=2000), showing naive fitting on selected data is unusable for future populations.
Limitations
- Experiments are restricted to two-stage selection and linear policies on small training sizes (N up to 3000).
- Real-world datasets are semi-synthetic because no multi-stage selection data exists; selection process is simulated.
- Solver time limit of 4 minutes means large-N solutions may not be optimal.
Experimental setup
Datasets: Adult German Credit COMPAS synthetic two-stage selection data
Benchmarks: Adult German Credit COMPAS synthetic two-stage selection data
Metrics: precision unfairness (equal opportunity disparity) constraint violation ratio training time
Baselines: No-IPW existing selection policy
Builds on: inverse probability weighting sample average approximation Rooney Rule analysis
Closest papers by meaning
- FairPFN: A Tabular Foundation Model for Causal Fairness (ICML 2025 · similarity 0.87)
- Fair Off-Policy Learning from Observational Data (ICML 2024 · similarity 0.87)
- Smooth Partial Lotteries for Stable Randomized Selection (NeurIPS 2026 · similarity 0.86)
- A Causal Lens for Learning Long-term Fair Policies (ICLR 2025 · similarity 0.86)
- Fair Classification with Partial Feedback: An Exploration-Based Data Collection Approach (ICML 2024 · similarity 0.85)
- Interventional Fairness on Partially Known Causal Graphs: A Constrained Optimization Approach (ICLR 2024 · similarity 0.85)
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