FedMABA: Using Multi-Armed Bandits to Improve Fairness in Federated Learning

Centrala begrepp

FedMABA is a novel federated learning algorithm that leverages multi-armed bandits to improve fairness by explicitly constraining performance disparities among clients with diverse data distributions, without compromising the server model's performance.

Sammanfattning

• Bibliographic Information: Wang, Z., Wang, L., Guo, Y., Zhang, Y.-J. A., & Tang, X. (2024). FedMABA: Towards Fair Federated Learning through Multi-Armed Bandits Allocation. arXiv preprint arXiv:2410.20141.
• Research Objective: This paper introduces FedMABA, a novel federated learning algorithm designed to address the challenge of performance unfairness among clients with diverse data distributions in federated learning.
• Methodology: FedMABA incorporates explicit constraints on client performance distribution into the optimization objective, utilizing the concept of adversarial multi-armed bandits to optimize a relaxed convex upper surrogate of the NP-hard problem. It employs a novel update strategy combining fair weights from loss variance constraints with average weights to ensure both fairness and server model performance.
• Key Findings:
  • The paper theoretically proves that constraining client performance disparities directly improves both the generalization performance of the server model and fairness in federated learning.
  • FedMABA demonstrates superior performance in enhancing fairness across different Non-IID scenarios on Fashion-MNIST, CIFAR-10, and CIFAR-100 datasets, while maintaining competitive server model performance.
  • The algorithm exhibits stability across different hyper-parameter settings.
• Main Conclusions: FedMABA offers a practical and effective solution for mitigating performance unfairness in federated learning, ensuring consistent performance across clients with diverse data distributions without sacrificing the overall model accuracy.
• Significance: This research significantly contributes to the field of fair federated learning by introducing a novel approach that directly addresses performance disparities among clients, a crucial aspect for ensuring fairness and practicality in real-world applications.
• Limitations and Future Research: While FedMABA shows promising results, future research could explore its robustness against malicious clients who might manipulate reported losses to gain undue advantage. Investigating its applicability in more complex federated learning scenarios with varying degrees of data heterogeneity and client participation patterns would further enhance its practical relevance.

Statistik

FedMABA achieves at least 33% better variance on Fashion-MNIST, 6% on CIFAR-10, and even 1.5x compared to the second-best baseline.
On CIFAR-100, FedMABA shows 8% better variance.

Citat

"In this work, we theoretically prove that the server model’s generalization error is upper bounded by client performance disparities. This shows that explicitly constraining performance disparities improves both the generalization performance of the server model and fairness in FL."
"Through MAB weights Allocation and aggregation approach, FedMABA enhances fairness while maintaining the convergence efficiency and generalization performance of the server model."

Viktiga insikter från

FedMABA: Towards Fair Federated Learning through Multi-Armed Bandits Allocation

by Zhichao Wang... på arxiv.org 10-29-2024

https://arxiv.org/pdf/2410.20141.pdf

Djupare frågor

How can FedMABA be adapted to address fairness in other federated learning settings beyond performance disparities, such as fairness in data representation or participation?

While FedMABA effectively addresses performance disparities in federated learning (FL), adapting it to tackle fairness concerns related to data representation or participation requires careful consideration and modifications:
1. Fairness in Data Representation:

Problem: Data representation bias arises when the data held by different clients reflects underlying societal biases, leading to models that perpetuate these biases.
FedMABA Adaptation:

Representation-Aware Rewards: Instead of solely using individual client performance (e.g., accuracy) as the reward signal for the Multi-Armed Bandit (MAB), incorporate metrics that quantify representation bias. This could involve measuring the model's performance across different demographic subgroups present in the data.
Constrained Optimization: Modify the optimization objective in FedMABA to include constraints that penalize models exhibiting significant performance disparities across sensitive subgroups. This encourages the MAB to prioritize clients whose data helps mitigate representation bias.
Data Augmentation and Balancing: Combine FedMABA with techniques like data augmentation (generating synthetic data to balance under-represented groups) or re-weighting client contributions based on their data diversity.
2. Fairness in Participation:

Problem: Clients with limited resources (e.g., low bandwidth, computational power) might participate less frequently, leading to models biased towards well-resourced clients.
FedMABA Adaptation:

Participation-Aware Rewards: Factor in client participation rates into the MAB reward mechanism. Clients who contribute more frequently could receive slightly lower rewards, encouraging the selection of less frequent participants.
Tiered Participation: Divide clients into tiers based on their resource availability. Implement separate MAB instances for each tier, ensuring that clients within a tier have a fair chance of selection.
Incentive Mechanisms: Integrate FedMABA with incentive mechanisms that reward clients for their participation, particularly those with limited resources. This can help level the playing field and promote more balanced participation.
Key Considerations:

Defining Fairness: Clearly define the specific fairness notion being addressed (e.g., demographic parity, equal opportunity) in the context of data representation or participation.
Metric Selection: Carefully choose appropriate metrics to quantify the chosen fairness notion and integrate them into the MAB reward or constraint formulation.
Trade-offs: Acknowledge potential trade-offs between fairness and other objectives like global model accuracy. Striking a balance is crucial.

Could focusing solely on performance disparity metrics inadvertently mask other underlying fairness issues within the data or model itself?

Yes, solely focusing on performance disparity metrics in FedMABA, while valuable, can inadvertently mask deeper fairness issues present within the data or the model itself. Here's why:

Data Bias Amplification: If the training data contains inherent biases (e.g., certain demographic groups are under-represented or mislabeled), optimizing solely for performance parity might lead to models that learn and amplify these biases. The model might achieve similar performance across clients by simply replicating existing societal prejudices.
Ignoring Subgroup Performance: Focusing on aggregate performance disparities can obscure significant performance differences among subgroups within the client population. For instance, a model might appear fair overall while still exhibiting bias against a specific demographic group that is consistently under-represented across clients.
Correlation, Not Causation: Performance disparities might be correlated with sensitive attributes (e.g., race, gender) without being directly caused by them. Focusing solely on these disparities might lead to interventions that fail to address the root causes of unfairness, which could lie in data collection practices, societal biases reflected in the data, or model design choices.
To mitigate these risks:

Comprehensive Fairness Assessment: Go beyond performance disparity metrics and conduct thorough fairness audits that examine the data, model, and outcomes across various sensitive attributes and subgroups.
Causal Analysis: Explore potential causal relationships between sensitive attributes and model performance to identify and address root causes of unfairness.
Transparency and Explainability: Employ techniques to make the model's decision-making process more transparent and explainable. This helps uncover hidden biases and build trust in the system.
Human-in-the-Loop: Incorporate human oversight and domain expertise to critically evaluate model fairness, particularly in sensitive applications.

How might the principles of fairness employed in FedMABA be applied to other distributed systems or collaborative learning environments beyond federated learning?

The fairness principles embedded in FedMABA, particularly its use of Multi-Armed Bandits (MAB) for fair resource allocation, can be extended to various distributed systems and collaborative learning environments:
1. Edge Computing and Resource Management:

Fair Task Allocation: In edge computing, where tasks are offloaded to edge devices with varying capabilities, an MAB-based approach like FedMABA can ensure fair task allocation. Devices with lower resources would be assigned less demanding tasks, preventing resource starvation and promoting overall system efficiency.
Bandwidth Allocation: In scenarios with limited bandwidth, an MAB can dynamically allocate bandwidth to different users or applications based on fairness criteria. This prevents bandwidth hogging and ensures a more equitable distribution of network resources.
2. Collaborative Filtering and Recommender Systems:

Fair Item Exposure: Recommender systems often suffer from popularity bias, where popular items get disproportionately recommended. An MAB can be used to balance item exposure, promoting fairness by giving less popular but potentially relevant items a chance to be recommended.
Diversity-Aware Recommendations: MABs can be designed to optimize for recommendation diversity, ensuring that users are exposed to a wider range of items or content, thereby mitigating filter bubbles and promoting fairness in content access.
3. Online Advertising and Auction Systems:

Fair Ad Allocation: In online advertising, an MAB can allocate ad slots fairly, considering both advertiser bids and fairness constraints. This prevents large advertisers from dominating the ad space and ensures that smaller advertisers have a fair opportunity to reach their target audience.
Preventing Discriminatory Targeting: MABs can be used to detect and mitigate discriminatory ad targeting practices by incorporating fairness constraints that prevent ads from being disproportionately shown to certain demographic groups.
Key Adaptations:

Contextual Information: Incorporate relevant contextual information into the MAB's decision-making process. For example, in edge computing, this could include device capabilities and task requirements.
Fairness Metrics: Define appropriate fairness metrics tailored to the specific application domain. These metrics should capture the desired notion of fairness in that context.
Exploration-Exploitation Trade-off: Carefully balance the MAB's exploration (trying out different options) and exploitation (choosing the best-performing options) to ensure both fairness and system efficiency.