Broadly, we are referring to machine-learning fairness; developing the benefits of machine learning for everyone.
In ML-fairness-gym, we aim to examine the implications of different decisions made when training algorithms and make it easier to see intended and unintended consequences of those decisions.
This version of ML-fairness-gym documentation assumes base knowledge about some common ML concepts.
The “gym” name is a reference to OpenAI Gym which is the basis for the environments in ML-fairness-gym. OpenAI’s Gym has been incredibly influential in popularizing simulation-based machine learning challenges and encouraging reproducible research in reinforcement learning. Many third party extensions of OpenAI’s Gym refer to gym somewhere in their names.
Take a look at our quick-start guide and how to use ML-fairness-gym in your research for some initial ideas. More examples can be found in the examples directory
Simulated environments are very useful for exploration. What seems like a policy that gives good outcomes with some parameters settings and initial conditions may in fact play out very differently with other settings.
Some of the most surprising results (e.g., [1,2,3,4]) in the research literature on fairness issues in machine learning have involved the implications of long term effects of various decision making rules, agents, or policies. ML-fairness-gym is intended to allow researchers to explore settings like this, where long term effects of decisions influence ML fairness outcomes, in simulated worlds that allow careful study, including the ability to examine the effects of varying key elements, examine counterfactual results, and perform easily replicable research in this fascinating area.
Experiments with simulated data are meant to augment experiments and tests with real data, not to replace them.
The environments in ML-fairness-gym are dynamic. That means that decisions made by your algorithm at step t affect the next decision it will be asked to make at time t+1.
This has a few implications: Data collection is part of the agent’s job and is not limited by how the dataset creators happened to collect their data. You can design agents that are more or less effective purely based on how they handle data collection. Metrics that assess every decision independently, like precision and recall, do not tell the full story because decisions affect each other.
In traditional datasets which involve decisions, you can only see one outcome based on the decision that was made at the time (e.g., no data on whether an applicant would have paid back a loan if they were not offered one). With simulations, this data can be calculated.
Another difference is that environments do not have a pre-specified “label” or a “goal”, rather it is up to the agents to decide what they will optimize for and how they will use the information.
When working with ML-fairness-gym, many of the decisions that are implicitly made in framing the problem as a classification problem (see e.g., discussions in Mitchell et al. Prediction-based decisions and fairness: A catalogue of choices, assumptions, and definitions) are made more explicit.
A drawback of working with simulations is that they are not “real data” and do not have the full distributional or dynamic complexity of real data. We do not try to simulate every effect of a decision in the real world, rather to use simple stylized examples to highlight the challenges that real dynamics could pose.
ML-fairness-gym environments currently replicate (and generalize) dynamics proposed in the following papers.
Lending Liu et al, Delayed Impact of Fair Machine Learning
Attention Allocation Ensign et al, Runaway Feedback Loops in Predictive Policing; Elzayn et al, Fair Algorithms for Learning in Allocation Problems
Strategic Manipulation Hu et al, The disparate effects of strategic manipulation; Milli et al, The Social Cost of Strategic Classification
ML-fairness-gym is for implementing stylized examples of scenarios where fairness concerns can arise. Although these examples are usually too simple to capture the full complexity of real deployment scenarios, they provide a number of unique opportunities to explore the properties of fair machine learning methods in practice. For example,
- Simulations allow researchers to explore how the moving parts in a machine learning deployment can interact to generate long term outcomes. These include censoring in the observation mechanism, errors from the learning algorithm, and interactions between the decision policy and environment dynamics.
- Simulations allow researchers to explore how well agents and external auditors can assess the fairness characteristics of certain decision policies based on observed data alone. These examples can be useful for motivating auxiliary data collection policies.
- Simulations can be used in concert with reinforcement learning algorithms to derive new policies with potentially novel fairness properties.
Yes and no. ML-fairness-gym environments can reveal interesting dynamics that apply in real-world scenarios, but these environments are stylized examples that do not capture the full complexity of real deployment scenarios. We recommend using ML-fairness-gym to characterize patterns or templates that you might then look for in real-world scenarios. We caution against taking the application that is used to motivate each environment (e.g., lending) too seriously - since these are small-scale abstracted simulations, they make simplifications and assumptions about reality. While the results from ML-fairness-gym can help provide intuition about agents in environments, and expose certain patterns of performance, they may differ from results obtained in the real world. For this reason we recommend the gym as a companion to evaluation with real world data and field tests.
Many ML-fairness-gym metrics can take, as input, a stratification function which takes a step of the history consisting of a state and action pair and returns stratification across the state variable of interest. The stratification function is left general enough to account for not only categorical group identification, but intersections as well.
(As always, in stratifying results, consider how sample size is affected, and interpret results with care, especially when determining which level of aggregation is appropriate. Cf. Simpson’s paradox.)
To create a new environment, start with the environments/template.py file. The template provides an outline to a FairnessEnv subclass, and describes what to fill in with TODO comments. For examples of already implemented environments, see the environments folder for:
If you would like to add your developed environment back to the ML-fairness-gym repo, please see the contributing doc.
The base agent class is in core.py. The agent class initializes
with a action_space and observation_space defined and provided by the
environment, it also takes an optional reward. To make your own agent, subclass
core.Agent and override the _act_impl() function. The only requirement on an
agent is that _act_impl() returns an action in action_space, and receives
observations in the observation_space.
For examples of agents, see the agents directory.
If you would like to add your developed agent back to the ML-fairness-gym repo, please see the contributing doc.
The base metric class is in core.py. To make your own metric,
subclass core.Metric and override the measure(env) function. For a simple
example of a metric that calculates the sum of a state variable over the
environment’s history, see SummingMetric in
value_tracking_metrics.py.
If you would like to add your developed metric back to the ML-fairness-gym repo, please see the contributing doc.
When implementing metrics, we look at the environment’s state, which is not fully visible to the agent during the training. This allows us to assess some counterfactuals like would the loan applicant have paid if they were given the loan.
The metric class also has a _simulate method which allows them to test at any
time point, what would have happened if another action had been taken.
This is one of the key benefits of ML-fairness-gym environments over more typical test / train splits that do not allow us to see the effect of taking a different path than happened to be chosen in the historical snapshot.
See core.py for more details.
ML-fairness-gym allows for the use of multiple metrics to evaluate a simulation and assess different notions of fairness. We encourage the use of multiple metrics to get a deeper understanding of the effect a policy has in a simulation.
run_simluation(env, agent, metrics, num_steps, seed) in
run_util.py accepts a list of metrics and evaluates all the
metrics at the end of a simulation. All example experiments in the
examples directory involve multiple metrics and can provide
examples of analysis with multiple metrics.
Since simulations presented or run as part of ML-fairness-gym can have different parameters, agents and metrics, the recommended way to report results is to provide a main file that can reproduce plots and results from your experiments. Examples of such main files can be found in the examples directory.
Providing the parameter settings for agent, environment, metrics, and the random seed(s) used is sufficient to replicate the results and allows others to meaningfully compare their own policies with the reported results.
There will not be leaderboards for different ML fairness problems. It is often difficult to compare different notions of fairness and success in regards to them. The goal of ML-fairness-gym is to provide a framework to allow individuals to explore problems via simulation to gain a deeper understanding of the effects of policies on different scenarios and their various implications for fairness over the long term.
Please cite:
Alexander D’Amour, Yoni Halpern, Hansa Srinivasan, Pallavi Baljekar, James Atwood, D. Sculley. Fairness is not Static: Deeper understanding of long term fairness via agents and environments. KDD workshop on Explainable AI (XAI) 2019.
Feel free to report bugs by creating github issues.
See CONTRIBUTING.md.
Some of the python code looks a little bit strange. Are you using type annotations? In many parts of the code base, we are using type annotations. You can read more about typing in python here. Another library we have found helpful for data classes and may be unfamiliar is the attrs library.
This is the initial version of the ML-fairness-gym (v 0.1.0) which focuses on recreating environments that have previously been discussed in research papers. The next version will have more environments and experiments.
[1] Lydia T Liu, Sarah Dean, Esther Rolf, Max Simchowitz, and Moritz Hardt. 2018. Delayed Impact of Fair Machine Learning. In Proceedings of the 35th International Conference on Machine Learning.
[2] Lily Hu, Nicole Immorlica, and Jennifer Wortman Vaughan. 2019. The disparate effects of strategic manipulation. In Proceedings of the Conference on Fairness, Accountability, and Transparency. ACM, 259–268.
[3] Smitha Milli, John Miller, Anca D Dragan, and Moritz Hardt. 2019. The Social Cost of Strategic Classification. In Proceedings of the Conference on Fairness, Accountability, and Transparency. ACM, 230–239.
[4] Danielle Ensign, Sorelle A Friedler, Scott Neville, Carlos Scheidegger, and SureshVenkatasubramanian. 2018. Runaway Feedback Loops in Predictive Policing. In Conference on Fairness, Accountability and Transparency. ACM, 160–171.