FairLMs

Fairness definitions and bias metrics for large language models — a companion library for studying and evaluating bias in LMs.

The long-term goal is a stable, sklearn-style API: import a metric, call compute(...), and get a result — without caring where the implementation lives.

Status: All 33 metrics share one contract — configuration in the constructor, data as a validated container passed to compute(model, data). Leaf main.py files and examples/ are short public-API demos. Implementation math still lives under fairlms/definition/.

Install

pip install fairlms

That's all most users need — fairlms is on PyPI, so installing does not require access to this repository.

The project is FairLMs; both the PyPI distribution and the import name are fairlms, all-lowercase per PEP 8.

Optional extras

pip install "fairlms[openai]"   # API-backed decoder metrics (CR, CTF, BA)
pip install "fairlms[dev]"      # pytest
pip install "fairlms[all]"      # openai + common extras

From source

To track unreleased work, or to develop the library:

git clone https://github.com/michaellarionov/FairLMs.git && cd FairLMs && pip install -e ".[dev]"

An editable install means your edits take effect immediately, with no reinstall. You can also install a specific commit or tag directly:

pip install "git+https://github.com/michaellarionov/FairLMs.git@v0.3.1"

Prefer a tag over @main if you do this: main tracks unreleased work, so any push can change behaviour under you. Tags don't move.

The import name is fairlms regardless of the repository name.

Requirements

Python ≥ 3.10 — the floor for torch, transformers and datasets.

Installed automatically: torch, transformers, datasets, numpy, pandas, scipy, scikit-learn, wordfreq, nltk. The last three are needed at import time by counterfactual_auc / normalized_position_distance, lexical_frequency_proportion, and morphological_choice_divergence respectively.

Versioning

Semantic versioning, currently pre-1.0 — the public API may still change between minor versions. The version is single-sourced in fairlms/_version.py; pyproject.toml reads it via [tool.setuptools.dynamic], so bump that one value.

To cut a release, bump _version.py, then tag. Pushing a v* tag triggers .github/workflows/publish.yml, which builds, validates with twine check --strict, checks the tag matches the version, and uploads to PyPI via Trusted Publishing (OIDC — no API token is stored anywhere):

git tag -a "v$(python scripts/package_version.py)" -m "Release" && git push origin --tags

Users then upgrade with pip install --upgrade fairlms.

Breaking changes

Metric calling conventions were not broken in 0.2.0: the previous keyword style (compute(model=m, T1_terms=[...])) still works and emits a DeprecationWarning naming its replacement. Those shims are scheduled for removal in a later release, so migrate when convenient.

Quick start

from fairlms.metrics import CrowSPairsScore, list_metrics
from fairlms.datasets import CrowSPairs
from fairlms.models import HuggingFaceModel

model = HuggingFaceModel("bert-base-uncased", task="mlm")
result = CrowSPairsScore().compute(model, CrowSPairs(n_max=50))
print(result.score, result.by_category)

# Discover metrics
print(list_metrics())

The contract

Every metric follows scikit-learn's estimator conventions:

Metric(**config).compute(model, data) -> MetricResult

• Configuration goes in the constructor, keyword-only, and is introspectable via get_params() / set_params() — so metrics can be cloned or swept.
• Data is the second positional argument: a FairnessDataset, a plain sequence, or a typed container from fairlms.metrics.data for metrics that need several labelled sets.
• Unknown keywords raise TypeError instead of silently using a default.

from fairlms.metrics import WEAT, SEAT, WordSets

words = WordSets(target_1=t1, target_2=t2, attribute_1=a1, attribute_2=a2)
WEAT(n_samples=10_000).compute(model, words)
SEAT(pooling="cls").compute(model, words)      # same data, different metric

WEAT(pooling="cls").get_params()               # {'n_samples': 10000, 'pooling': 'cls'}

The published association tests ship pre-wrapped in fairlms.data, so a standard run needs no term lists at all — and swapping the checkpoint does not change the call:

from fairlms.data import weat_c1, list_word_sets
from fairlms.metrics import SEAT
from fairlms.models import HuggingFaceModel

metric = SEAT(n_samples=1_000)
for ckpt in ("bert-base-uncased", "roberta-base"):
    result = metric.compute(HuggingFaceModel(ckpt, task="encoder"), weat_c1)
    print(ckpt, result.score, result.details["p_value"])

list_word_sets()   # ['weat_c1', …, 'seat_c1', …]

weat_c1 is a WordSets, so user-supplied evidence goes through the exact same call with no adapter code:

mine = WordSets(target_1=names_a, target_2=names_b,
                attribute_1=pleasant, attribute_2=unpleasant)
metric.compute(model, mine)

Containers validate at construction, so mistakes fail immediately:

>>> ContextSets(["a sentence"], ...)
TypeError: target_1 must be a mapping of term -> list of context sentences, got
list. (A flat list of sentences is not accepted; CEAT samples contexts per term,
so terms must be keyed.)

Metrics that need no model

Five metrics score predictions you already have. They also exist as plain functions, mirroring sklearn.metrics:

from fairlms.metrics import equal_opportunity_gap, accuracy_disparity

equal_opportunity_gap(y_true, y_pred, groups, g1="A", g2="B")   # -> float
accuracy_disparity(scores_stereotype, scores_counter)           # -> float

Also available: inference_bias_score, fair_inference_score, context_based_disparity. Use the class form (EqualOpportunityGap, …) when you want the full MetricResult with diagnostics.

Dataset diagnostics

Dataset diagnostics are a separate, dataset-first API. They consume explicit evidence and audit intent rather than a model, and return a structured report whose components can be ready, blocked, or not_applicable. Missing evidence is never represented as a score of zero.

The first diagnostic is axis-level representativeness (b_rep): smoothed KL(observed || reference) in nats. It requires an explicit reference and its provenance; the package does not infer a population prior from a dataset name.

from fairlms.diagnostics import (
    DatasetAuditSpec,
    ReferenceDistribution,
    RepresentationEvidence,
    audit_representativeness,
)

evidence = RepresentationEvidence(
    axis="community",
    counts={"amber": 3, "teal": 1},
    source="My benchmark, evaluation split",
)
reference = ReferenceDistribution(
    axis="community",
    probabilities={"amber": 0.5, "teal": 0.5},
    source="Benchmark design specification v1",
    purpose="design_target",
    population="Intended benchmark composition",
)
spec = DatasetAuditSpec(
    target_name="my-unregistered-benchmark",
    target_kind="benchmark_dataset",
    task_family="free_text",
    design_stance="stress_test",
    references={"community": reference},
)

report = audit_representativeness(evidence, spec)
result = report.components["b_rep"]
print(result.status.value, result.value)
print(report.to_json())

population_proxy and stress_test use the same mathematics but not the same interpretation. A stress test may deliberately over-sample a category; the report therefore warns that divergence is descriptive evidence rather than an automatic fairness failure. Use RepresentationEvidence.from_records(...) or .from_dataframe(...) with explicit field names, support, and optional value mapping for unfamiliar schemas. Adapters preserve the complete JSON-safe value mapping in provenance so a recoding can be reproduced. Reference probabilities outside an absolute 1e-9 sum tolerance are rejected; values inside that tolerance are canonicalized onto the probability simplex and the report records both the input sum and whether canonicalization occurred.

Start with Preparing audit evidence for the evidence-layer boundary and input checklist. The detailed representativeness guide covers supported input paths, raw text, coverage, references, and a complete b_rep example.

Scoring instrument audits

Scorer diagnostics audit scores that already exist at row level. They do not infer groups from raw text or run a model/scorer to generate scores. score_mean_gap is the descriptive maximum absolute group-mean difference in the scorer's native score units. score_rate_gap first applies one explicit, serialized score-to-event rule to every group, then reports the maximum absolute group event-rate difference as a proportion. score_wasserstein_1_gap compares the complete one-dimensional empirical score distributions and reports their maximum pairwise Wasserstein-1 distance in the scorer's native score units. score_counterfactual_sensitivity separately averages absolute score changes inside complete, explicitly declared two-condition pairs.

from fairlms.diagnostics import (
    DatasetAuditSpec,
    ScoreRateTransform,
    ScoredGroups,
    ScorerMeanGap,
    ScorerRateGap,
    ScorerWasserstein1Gap,
    audit_scores,
)

evidence = ScoredGroups(
    axis="cohort",
    groups=("amber", "amber", "teal", "teal"),
    scores=(0.1, 0.3, 0.8, 1.0),
    score_name="example_safety_score",
    source="Existing row-level score export v1",
    score_range=(0.0, 1.0),
)
rate_transform = ScoreRateTransform(
    event_name="score_at_or_above_policy_threshold",
    threshold=0.5,
    direction="higher",
    inclusive=True,
    provenance={"rule_source": "Example policy v1"},
)
spec = DatasetAuditSpec(
    target_name="example-score-table",
    target_kind="score_table",
    task_family="scored_rows",
    design_stance="stress_test",
    references={},
    requested_components=(
        "score_mean_gap",
        "score_rate_gap",
        "score_wasserstein_1_gap",
    ),
)

report = audit_scores(
    evidence,
    spec,
    diagnostics=(
        ScorerMeanGap(),
        ScorerRateGap(transform=rate_transform),
        ScorerWasserstein1Gap(),
    ),
)
mean_result = report.components["score_mean_gap"]
rate_result = report.components["score_rate_gap"]
w1_result = report.components["score_wasserstein_1_gap"]
print(mean_result.value, mean_result.details["unit"])  # 0.7 score_units
print(rate_result.value, rate_result.details["unit"])  # 1.0 proportion
print(w1_result.value, w1_result.details["unit"])  # 0.7 score_units

Paired sensitivity uses independent evidence because group marginals do not preserve which rows are counterparts:

from fairlms.diagnostics import (
    PairedScores,
    ScorerCounterfactualSensitivity,
)

paired = PairedScores(
    axis="declared_identity_intervention",
    pair_ids=("p1", "p1", "p2", "p2"),
    conditions=("baseline", "swap", "baseline", "swap"),
    scores=(0.1, 0.4, 0.8, 0.3),
    condition_roles=("baseline", "swap"),
    score_name="example_safety_score",
    source="Existing paired score export v1",
    pairing_basis="Reviewed minimal identity-token substitutions",
    score_range=(0.0, 1.0),
)
paired_spec = DatasetAuditSpec(
    target_name="example-paired-score-table",
    target_kind="score_table",
    task_family="paired_sentences",
    design_stance="stress_test",
    references={},
    requested_components=("score_counterfactual_sensitivity",),
)
paired_report = audit_scores(
    paired,
    paired_spec,
    diagnostic=ScorerCounterfactualSensitivity(),
)
print(paired_report.components["score_counterfactual_sensitivity"].value)  # 0.4

There is no implicit threshold, direction, or boundary rule. score_range validates scores; it is neither a threshold nor a Wasserstein normalization. A missing rate transform is blocked, not a zero gap. Mean, rate, and W1 gaps answer different questions, and none is a causal claim, fairness pass/fail rule, or error-rate metric. Paired sensitivity supports identity-isolated causal language only if the pairs really differ solely in the declared intervention; the package validates pair completeness but cannot verify that semantic claim from scores. W1 and paired sensitivity are symmetric primary values and carry no higher/lower direction. higher plus inclusive=True is the paper-exact score >= threshold definition; the report marks lower-tail and exclusive-boundary variants separately. Treat each value as a per-dataset, per-scorer diagnostic, and rate gaps additionally as per-rule, rather than using them to rank datasets or unrelated scorer scales. See Preparing audit evidence and the runnable score_rate_gap and score_wasserstein_1_gap and score_counterfactual_sensitivity examples.

Shared loaders:

from fairlms.datasets import CrowSPairs, BBQ, StereoSet
from fairlms.models import load_masked_lm

crows = CrowSPairs().load()
bbq = BBQ(categories=["Age"]).load()
loaded = load_masked_lm("bert-base-uncased")

Leaf runners under definition/ are short demos of the same public API:

python -m fairlms.definition.encoder_only.intrinsic_bias.probability_based.pseudo_log_likelihood_metrics.cps.main

See also examples/ at the repository root.

Package layout

fairlms/
├── metrics/        # Public API: CrowSPairsScore, WEAT, … (all expose compute)
│   ├── data.py     #   Validated input containers (WordSets, ProbeSet, …)
│   └── functional.py #  sklearn.metrics-style functions (model-free metrics)
├── diagnostics/    # Dataset/result-table evidence, applicability, and reports
├── datasets/       # CrowSPairs, StereoSet, BBQ, BiasInBios, WinoBias, …
├── models/         # HuggingFaceModel, OpenAIModel, load_* helpers
├── utils/          # PLL / masking / association / path helpers
├── data/           # Bundled CrowS-Pairs + BBQ files; exports WEAT/SEAT word sets
├── artifacts/      # Preferred output dir for metric CSVs
└── definition/     # Internal implementations + short public-API demos (main.py)

Repo-root examples/ has additional runnable snippets.

Every metric exposes the same method: compute(...).

Datasets

Loaders prefer canonical files in fairlms/data/, then fall back to legacy copies under definition/ so existing scripts keep working.

Bundled word sets

Association tests need four labelled term lists rather than a corpus, so they are importable constants instead of loader classes. Each one is an already-validated WordSets, ready to pass straight to compute:

from fairlms.data import weat_c2, get_word_set, WORD_SET_LABELS

get_word_set("seat_c1")                # same objects, by name
WORD_SET_LABELS["weat_c2"]             # 'C2 – Gender (Male/Female names × Career/Family)'

Both families work with WEAT and SEAT; the seat_* lists are the larger name sets the sentence templates were sized for. All eight have balanced target lists, which SEAT requires. CEAT is not included — it consumes ContextSets (terms keyed to context sentences), not four flat lists.

Models

from fairlms.models import (
    HuggingFaceModel,
    load_masked_lm,      # task="mlm"
    load_encoder,        # task="encoder"
    load_sequence_classifier,
    load_seq2seq,
    load_causal_lm,
    OpenAIModel,
)

HuggingFaceModel("roberta-base", task="sequence_classification").load()
OpenAIModel("davinci-002").load()  # needs OPENAI_API_KEY; pip install fairlms[openai]

Set HF_TOKEN (or HUGGING_FACE_HUB_TOKEN) for gated models such as Llama-2.

Design principles

1. One verb for metrics — compute (sklearn’s fit / predict analogue).
2. Separate metrics from datasets — reuse the same metric on CrowS-Pairs, StereoSet, or custom data.
3. Stable public surface — internals under definition/ can change without breaking user code.
4. Book-aligned taxonomy — definition/{encoder_only,encoder_decoder,decoder_only}/{intrinsic_bias,extrinsic_bias}/… mirrors the conceptual organization of the accompanying textbook.
5. Applicability before computation — dataset diagnostics report missing or incompatible evidence instead of manufacturing a numeric result.

Development

pip install -e ".[dev]"
pytest                  # contract suite over every metric in the registry
# Run a leaf metric script:
python -m fairlms.definition.encoder_only.intrinsic_bias.similarity_based.weat.main

tests/test_common.py is the analogue of scikit-learn's check_estimator: it runs the parameter/repr/keyword contract across METRIC_REGISTRY, so a new metric that breaks the shape fails there rather than surprising a user. It needs no network or model weights.

Tests that do need model weights skip cleanly when the weights aren't cached, so the suite is hermetic:

HF_HUB_OFFLINE=1 pytest -q     # what CI runs; a few seconds, no downloads

CI (.github/workflows/test.yml) runs this on Python 3.10 and 3.13 for every push and pull request. A second clean-install job builds the wheel, installs it into a fresh environment, and imports it from a directory with no source checkout on sys.path.

That second job exists because an editable install cannot catch a whole class of packaging bug: fairlms.metrics eagerly imports every metric family, so any third-party module imported at module scope under fairlms/definition/ is a hard requirement of import fairlms. If such a dependency is only listed in an extra, pip install fairlms produces a package that cannot be imported — while every local test still passes, because the developer's environment already has it. tests/test_packaging.py also guards this statically, walking the AST and naming the offending file.

Publishing an edit

Edits reach users through a tagged release, not through main:

1. Edit locally — your editable install picks changes up immediately.
2. pytest — the contract suite catches API breakage before it ships.
3. Commit and push. CI verifies the matrix and the clean install.
4. Bump fairlms/_version.py, then tag and push the tag.
5. The publish workflow uploads to PyPI; users get it with pip install --upgrade fairlms.

Metric result CSVs should go under fairlms/artifacts/ (via fairlms.utils.results_to_csv); leaf-local *_results.csv files are gitignored.

License

MIT