We view fairness as a property of distributional stability. Rather than assessing a predictor under a fixed data distribution, we study how its predictions change under perturbations that modify the composition of protected groups. A predictor is fair if it remains stable under such shifts. Under this perspective, several classical notions of fairness arise as stability with respect to specific perturbations, with the associated unfairness gap given by a Lipschitz constant of a prediction-rate functional. This formulation also yields guarantees that hold uniformly over a range of demographic compositions at test time, without requiring knowledge of the deployment distribution. It leads to a learning procedure based on convex combinations of reweighted predictors, formulated as a second-order cone program, for which we establish generalization bounds. Experiments on standard benchmarks illustrate the approach.
Figures & tables
Adult
COMPAS
Constraint
Model
U(h)↓
Deploy gap ↓
Accuracy ↑
U(h)↓
Deploy gap ↓
Accuracy ↑
DP
ERM
.180±.005
.122±.003
.845±.002
.132±.009
.079±.006
.680±.007
ERM+DP
.036±.006
.049±.006
.827±.002
.012±.006
.011±.004
.566±.019
PostProc
.013±.009
.097±.005
.823±.004
.038±.021
.044±.022
.555±.016
Shifty
.033±.021
.138±.032
.802±.010
.015±.012
.472±.039
.510±.007
STABLE
.011±.000
.006±.000∗
.753±.003
.012±.001
.006±.001∗
.680±.009∗
Table 1 : Results on the Adult Income and COMPAS datasets (mean ± std over 20 seeds). The deploy gap is supπ′∈{0,1}∣Φ(h;π′)−t∣ . Bold indicates the best value per column, constraint, and dataset. "*" indicates statistical significance when compared with the second-best result (underlined). Significance is assessed via paired Wilcoxon signed-rank tests. ERM is reported for reference only.
Figure 1 : Prediction rate Φ(h;π′) under demographic shift on the Adult Income and COMPAS datasets for DP and EO. Shaded regions show ± std of the curve shape over 20 random seeds.
Figure 2 : Geographic generalization on ACS Income. (left) Prediction rate Φ(h;πstate) as a function of the state proportion of White residents. Dashed lines show linear fits per method; (right) Accuracy vs. DP unfairness gap U(h) across held-out states. Each point corresponds to one state.
Appendix figures & tables6 assets
Supplementary material from the paper’s appendix.
Appendix
p1\πˉ
0.1
0.2
0.3
0.2
1.15
0.83
0.58
0.3
0.79
0.53
0.34
0.5
0.37
0.19
0.08
Appendix
Table 2 : Minimum DRO radius ε∗(πˉ) required to cover all demographic shifts π′∈[πˉ,1−πˉ] , for varying training group proportion p1 and perturbation lower bound πˉ .
ERM + constraint
STABLE (ours)
PostProc
Shifty
DP
EO
DP
EO
DP
EO
DP
EO
Adult
3.5±0.39
5.06±1.35
4.98±0.56
6.41±0.6
1.6±0.1
1.85±0.07
284.34±314.12
269.8±165.8
COMPAS
1.01±0.18
1.01±0.27
1.66±0.52
1.69±0.27
1.12±0.07
1.25±0.08
11.67±4.9
16.98±6.56
ACS
126.8±12
101.2±15.8
151.2±11.1
149.9±10.3
8.38±0.67
17.0±1.6
56.9±11.6
50.2±9.8
Appendix
Table 3 : Average training time per seed (seconds). All experiments run locally on an Apple M2, 16 GB RAM, macOS. Shifty uses Setting 2 (unknown demographic shift, α=0.25 ). NA stands for Not Applicable.
Figure 3 : Hyperparameter sensitivity on the Adult dataset (DP constraint, seed 0). Each cell reports the value of accuracy (left), U(h) (center) and deploy gap max(∣Φ(h;0)−t∣,∣Φ(h;1)−t∣) (right) as a function of threshold δ and the perturbation lower bound πˉ .
Adult
COMPAS
ACS Income
DP
EO
DP
EO
DP
EO
πˉ
0.02
0.15
0.02
0.15
0.02
0.15
δ
10−5
10−5
10−5
10−4
10−5
10−5
Appendix
Table 4 : Selected hyperparameters for STABLE. K=30 and m=60 are fixed across all settings. N.A. stands for Not Applicable.
Figure 4 : Geographic generalization on ACS Income. (left) Prediction rate Φ(h;πstate) as a function of the state proportion of White residents. Dashed lines show linear fits per method; (right) Accuracy vs. EO unfairness gap U(h) across held-out states. Each point corresponds to one state.
Mathematics Department, The Hong Kong University of Science and Technology, Hong Kong, China · Department of Statistics and Data Science, University of Pennsylvania, Philadelphia, PA, USA.