# Fairness Lens

> Evaluates and designs systems for equitable treatment across relevant subgroups

- **Category**: Machine Learning
- **Subcategory**: Trust, Evaluation and Responsible AI
- **Canonical URL**: https://designpattern.fyi/machine_learning/fairness-lens/

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## Description
**Intent**: Prevent models from learning and amplifying unfair patterns against particular groups by deliberately evaluating and designing systems for equitable treatment across relevant subgroups.

**Context**: Models trained on real-world, often historically biased data can learn and amplify unfair patterns. Optimizing purely for aggregate accuracy can mask badly disparate performance across subgroups, producing outcomes that are unfair, legally risky, and harmful.

**Solution**: Deliberately evaluate and design the system—data collection, problem framing, feature choices, outputs, and evaluation—for equitable treatment across relevant subgroups. Use established fairness metrics (demographic parity, equal opportunity, equalized odds) and apply mitigations at appropriate stage (data, model, or output).



## Use Cases
- Models affecting people (hiring, lending, healthcare)
- Domains with legal fairness requirements
- Systems with history of discrimination concerns
- Any high-stakes prediction affecting diverse populations






## Trade-offs


### Advantages

- Identifies and mitigates unfair performance disparities

- Addresses legal and ethical requirements

- Prevents harmful amplification of historical bias

- Enables transparent fairness evaluation




### Considerations & Drawbacks

- Fairness metrics can conflict with each other and accuracy

- Requires real value judgments and stakeholder consultation

- Not purely an engineering fix—requires ethical decisions

- Ongoing evaluation needed as data drift can introduce disparities







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**Reference**: [Original Source](https://github.com/GoogleCloudPlatform/ml-design-patterns)