augsynth-py

A Python implementation of Augmented Synthetic Control Methods and geo-experimentation tooling. Methodologically faithful to the published literature, validated against the R reference implementations.

Status: alpha. The estimator API is functional and validated against R, but not yet stable across releases. Pin the exact version in production.

What this is

Synthetic control methods for causal inference, with a focus on the use case that matters most in modern marketing science: measuring the lift of geo-level ad campaigns. The roadmap targets feature parity with:

• The R augsynth package (estimators).
• Meta's R GeoLift package (orchestration: power analysis, market selection, multi-cell).

Why another synthetic control package

There are good Python options for parts of this problem (CausalPy, pysyncon, tfcausalimpact), but none provides Augmented Synthetic Control Methods (Ben-Michael, Feller & Rothstein 2021) together with the GeoLift-style orchestration layer in a single Python-native package.

Installation

pip install augsynth-py

For the validation test suite (requires R and the augsynth R package):

pip install "augsynth-py[validation]"

Environments pinned to numpy 1.x

Both numpy 1.26+ and numpy 2.x are supported. When augsynth-py shares an environment with libraries that cannot move off numpy 1.x yet (econml, tslearn/numba, and similar), install the numpy1 extra, which resolves the dependency set against the last releases built for that ABI:

pip install "augsynth-py[numpy1]"

pip only reconciles what a single command names, so when augsynth-py is added to an environment that already holds such pins, state them explicitly — in the same command or through a constraints file:

# constraints.txt
numpy>=1.26.4,<2
cvxpy>=1.4.1,<1.5

pip install -c constraints.txt augsynth-py

The oldest supported dependency set — numpy 1.26, scipy 1.12, cvxpy 1.4.1, polars 1.0, joblib 1.3 on Python 3.11 — runs the unit suite on every push. See docs/compatibility.md for the full matrix.

Quickstart

import numpy as np
import polars as pl

from augsynth_py import AugSynth, conformal_pvalue

# Simulated geo panel: 20 markets x 90 days, +10% lift in geo_00 from day 70.
rng = np.random.default_rng(7)
days = np.arange(90)
base = rng.uniform(80, 120, 20)
trend = rng.normal(0.1, 0.05, 20)
seasonal = 5 * np.sin(2 * np.pi * days / 7)

panel = pl.concat(
    pl.DataFrame(
        {
            "geo": f"geo_{i:02d}",
            "day": days,
            "sales": base[i] + trend[i] * days + seasonal + rng.normal(0, 1.0, 90),
        }
    )
    for i in range(20)
).with_columns(
    pl.when((pl.col("geo") == "geo_00") & (pl.col("day") >= 70))
    .then(pl.col("sales") * 1.10)
    .otherwise(pl.col("sales"))
    .alias("sales")
)

fit = AugSynth(lambda_=1.0).fit(
    panel,
    unit="geo",
    time="day",
    outcome="sales",
    treated="geo_00",
    treatment_time=70,
)

print(f"ATT: {fit.att_:.2f} ({fit.att_pct_:+.1%})")
# ATT: 10.29 (+9.8%)

# The noise in this simulated panel is iid; on real (autocorrelated) series
# keep the default permutation_type="block".
p = conformal_pvalue(fit, permutation_type="iid", rng=np.random.default_rng(0))
print(f"conformal p-value: {p:.4f}")
# conformal p-value: 0.0120

Treating more than one market

treated takes either a single unit value or any iterable of them — list, tuple, set, np.ndarray, pl.Series. An iterable designates a treated group: the units are collapsed to their elementwise mean and dropped from the donor pool, so att_ is the effect on that group mean.

group_fit = AugSynth(lambda_=1.0).fit(
    panel,
    unit="geo",
    time="day",
    outcome="sales",
    treated={"geo_00", "geo_01"},  # <- a group, not a single market
    treatment_time=70,
)

print(group_fit.units_[0])
# geo_00,geo_01

print(f"ATT on the group mean: {group_fit.att_:.2f}")
# ATT on the group mean: 4.83
# (lower than the 10.29 above because only geo_00 got the lift; geo_01 dilutes it)

str and bytes are the one exception: they are read as a single unit value, not as a sequence of characters. To treat exactly one market, either form works (treated="geo_00" or treated=["geo_00"]).

The aggregate lift across the group is att_ * n_treated * n_post_periods — att_ itself stays per-unit-per-period, so it is comparable to a single-market fit.

What's available today:

• Synth — classical simplex-constrained synthetic control (outcome-only form, augsynth(progfunc = "None", scm = TRUE) analogue), with optional unit fixed effects.
• AugSynth — ridge-augmented synthetic control (Ben-Michael, Feller & Rothstein 2021), with leave-one-out CV for the ridge penalty by default.
• conformal_pvalue / conformal_interval — exact conformal inference for a constant post-period effect (Chernozhukov, Wuthrich & Zhu 2021), block and iid permutation schemes.
• Multi-treated fits: pass an iterable of units as treated to estimate the effect on the treated-group mean (see Treating more than one market).

The GeoLift-style orchestration layer (power analysis, market selection) is the next milestone on the roadmap.

Methodological references

The implementation is based on the published literature, not translated from the R sources. Key references:

• Abadie, Diamond & Hainmueller (2010). Synthetic Control Methods for Comparative Case Studies. JASA.
• Ben-Michael, Feller & Rothstein (2021). The Augmented Synthetic Control Method. JASA.
• Xu (2017). Generalized Synthetic Control Method. Political Analysis.
• Chernozhukov, Wuthrich & Zhu (2021). An Exact and Robust Conformal Inference Method for Counterfactual and Synthetic Controls. JASA.

See docs/methodology.md for the mapping between code and equations.

Validation against R

Every estimator in this package is validated numerically against the R reference implementation. The validation suite lives in tests/validation_against_r/ and runs as a separate CI job.

If you find a discrepancy with the R output beyond documented tolerances, please open an issue — that is a bug.

Contributing

Read CLAUDE.md first. It contains the architectural decisions, coding conventions, and the validation rule that PRs must satisfy.

License

MIT. See LICENSE.