FairTorch

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FairTorch won 1st prize at the Global PyTorch Summer Hackathon 2020, Responsible AI section.

PyTorch implementation of parity loss as constraints function to realize the fairness of machine learning.

Demographic parity loss and equalied odds loss are available.

This project is a part of PyTorch Summer Hackathon 2020. visit our project page.

Usage

dp_loss = DemographicParityLoss(sensitive_classes=[0, 1], alpha=100)
criterion = nn.BCEWithLogitsLoss()

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.
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logit = model(x_train)
loss = criterion(logit.view(-1), y_train)
loss = loss + dp_loss(x_train, logit, sensitive_features)

Install

pip version

pip install fairtorch

newest version

git clone https://github.com/MasashiSode/fairtorch
cd fairtorch
pip install .

Background

In recent years, machine learning-based algorithms and softwares have rapidly spread in society. However, cases have been found where these algorithms unintentionally suggest discriminatory decisions[1]. For example, allocation harms can occur when AI systems extend or withhold opportunities, resources, or information. Some of the key applications are in hiring, school admissions, and lending[2]. Since Pytorch didn't have a library to achieve fairness yet, we decided to create one.

What it does

Fairtorch provides tools to mitigate inequities in classification and regression. Classification is only available in binary classification. A unique feature of this tool is that you can add a fairness constraint to your model by simply adding a few lines of code.

Challenges we ran into

In the beginning, we attempted to develop FairTorch based on the Fairlearn[3]’s reduction algorithm. However, it was implemented based on scikit-learn and was not a suitable algorithm for deep learning. It requires ensemble training of the model, which would be too computationally expensive to be used for deep learning. To solve that problem, we implemented a constrained optimization without ensemble learning to fit the existing Fairlearn algorithm for deep learning.

How we built it

We employ a method called group fairness, which is formulated by a constraint on the predictor's behavior called a parity constraint, where <img src="https://latex.codecogs.com/png.latex?X" title="X" /> is the feature vector used for prediction, <img src="https://latex.codecogs.com/png.latex?A" title="A" /> is a single sensitive feature (such as age or race), and <img src="https://latex.codecogs.com/png.latex?Y" title="Y" /> is the true label. A parity constraint is expressed in terms of an expected value about the distribution on <img src="https://latex.codecogs.com/png.latex?(X,&space;A,&space;Y)" title="(X, A, Y)" />.

In order to achieve the above, constrained optimization is adopted. We implemented loss as a constraint. The loss corresponds to parity constraints.

Demographic Parity and Equalized Odds are applied to the classification algorithm.

We consider a binary classification setting where the training examples consist of triples <img src="https://latex.codecogs.com/png.latex?(X,&space;A,&space;Y)" title="(X, A, Y)" />, where X is a feature value, $A$ is a protected attribute, and <img src="https://latex.codecogs.com/png.latex?Y&space;\in&space;{0,&space;1}" title="Y \in {0, 1}" /> is a label.A classifier that predicts <img src="https://latex.codecogs.com/png.latex?X" title="Y" /> from <img src="https://latex.codecogs.com/png.latex?X" title="X" /> is <img src="https://latex.codecogs.com/png.latex?h:&space;X&space;\rightarrow&space;Y" title="h: X \rightarrow Y" />.

The demographic parity is shown below.

<img src="https://latex.codecogs.com/png.latex?E[h(X)|&space;A=a]&space;=&space;E[h(X)]&space;\&space;\rm{for&space;\&space;all}&space;\&space;a&space;\in&space;A" title="E[h(X)| A=a] = E[h(X)] \ \rm{for \ all} \ a \in A" />

Next, the equalized odds are shown below.

<img src="https://latex.codecogs.com/png.latex?E[h(X)|&space;A=a,&space;Y=y]&space;=&space;E[h(X)|Y=y]&space;\&space;\rm{for&space;\&space;all}&space;\&space;a\in&space;A,&space;\&space;y&space;\in&space;Y" title="E[h(X)| A=a, Y=y] = E[h(X)|Y=y] \ \rm{for \ all} \ a\in A, \ y \in Y" />

We consider learning a classifier <img src="https://latex.codecogs.com/png.latex?h(X;&space;\theta)" title="h(X; \theta)" /> by pytorch that satisfies these fairness conditions. The <img src="https://latex.codecogs.com/png.latex?\theta" title="\theta" /> is a parameter. As an inequality-constrained optimization problem, we convert (1) and (2) to inequalities in order to train the classifier.

<img src="https://latex.codecogs.com/png.latex?M&space;\mu&space;(X,&space;Y,&space;A,&space;h(X,&space;\theta))&space;\leq&space;c" title="M \mu (X, Y, A, h(X, \theta)) \leq c" />

Thus, the study of the classifier <img src="https://latex.codecogs.com/png.latex?h(X;&space;\theta)" title="h(X; \theta)" /> is as follows. <img src="https://latex.codecogs.com/png.latex?\rm{Min}_{\theta}" title="\rm{Min}_{\theta}" />s error <img src="https://latex.codecogs.com/png.latex?(X,&space;Y)" title="(X, Y)" /> subject to <img src="https://latex.codecogs.com/png.latex?M" title="M" /> <img src="https://latex.codecogs.com/png.latex?\mu&space;(X,&space;Y,&space;A,&space;h(X,&space;\theta))&space;\leq&space;c" title="\mu (X, Y, A, h(X, \theta)) \leq c" /> To apply this problem to pytorch's gradient method-based parameter optimization, we make the inequality constraint a constraint term R.

<img src="https://latex.codecogs.com/png.latex?R&space;=&space;B&space;\cdot&space;|ReLU(M&space;\mu&space;(X,&space;Y,&space;A,&space;h(X,&space;\theta))&space;-&space;c)|^2" title="R = B \cdot |ReLU(M \mu (X, Y, A, h(X, \theta)) - c)|^2" />

Accomplishments that we're proud of

We confirmed by experiment that inequality is reduced just adding 2 lines of code.

What We learned

What we learn is how to create criteria of fairness, the mathematical formulations to achieve it.

What's next for FairTorch

As the current optimization algorithm is not yet refined in FairTorch, we plan to implement a more efficient constrained optimization algorithm. Other definitions of fairness have also been proposed besides demographic parity and equalized odds. In the future, we intend to implement other kinds of fairness.

References

1. the keynote by K. Crawford at NeurIPS 2017
2. A Reductions Approach to Fair Classification (Alekh Agarwal et al.,2018)
3. Fairlearn: A toolkit for assessing and improving fairness in AI (Bird et al., 2020)

Development

poetry install

Test

pytest

Authors

• Akihiko Fukuchi
• Yoko Yabe
• Masashi Sode

Contributors ✨

Thanks goes to these wonderful people (emoji key):

<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section --> <!-- prettier-ignore-start --> <!-- markdownlint-disable --> <table> <tr> <td align="center"><a href="https://www.masashisode.com"><img src="https://avatars.githubusercontent.com/u/39261814?v=4?s=100" width="100px;" alt=""/><br />_{<b>Masashi Sode</b>}</a><br /><a href="#infra-MasashiSode" title="Infrastructure (Hosting, Build-Tools, etc)">🚇</a> <a href="https://github.com/wbawakate/fairtorch/commits?author=MasashiSode" title="Tests">⚠️</a> <a href="https://github.com/wbawakate/fairtorch/commits?author=MasashiSode" title="Code">💻</a> <a href="#maintenance-MasashiSode" title="Maintenance">🚧</a> <a href="#tutorial-MasashiSode" title="Tutorials">✅</a> <a href="https://github.com/wbawakate/fairtorch/pulls?q=is%3Apr+reviewed-by%3AMasashiSode" title="Reviewed Pull Requests">👀</a></td> <td align="center"><a href="https://github.com/akiFQC"><img src="https://avatars.githubusercontent.com/u/32811500?v=4?s=100" width="100px;" alt=""/><br />_{<b>Aki_FQC</b>}</a><br /><a href="https://github.com/wbawakate/fairtorch/commits?author=akiFQC" title="Code">💻</a> <a href="https://github.com/wbawakate/fairtorch/commits?author=akiFQC" title="Tests">⚠️</a> <a href="#maintenance-akiFQC" title="Maintenance">🚧</a></td> <td align="center"><a href="https://github.com/ykt345"><img src="https://avatars.githubusercontent.com/u/3901603?v=4?s=100" width="100px;" alt=""/><br />_{<b>yoko yabe</b>}</a><br /><a href="#projectManagement-ykt345" title="Project Management">📆</a> <a href="#ideas-ykt345" title="Ideas, Planning, & Feedback">🤔</a></td> </tr> </table> <!-- markdownlint-restore --> <!-- prettier-ignore-end --> <!-- ALL-CONTRIBUTORS-LIST:END -->

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