causalem 0.6.2

Causal Inference using Ensemble Matching

CausalEM – Ensemble Matching for Causal Inference

CausalEM is a toolbox for multi-arm treatment‑effect estimation using stochastic matching and a stacked ensemble of heterogeneous ML models. It supports continuous, binary, and survival outcomes.

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Key Features

1. Stochastic nearest-neighbor (NN) matching -> Larger effective sample size (ESS) and improved TE estimation accuracy compared to standard (deterministic) NN matching.
2. G-computation using two-staged, stacked ensemble of hetrogeneous learners -> Generalization of standard G-computation framework to ensemble learning; cross-fitting of propensity-score and outcome models, similar to DoubleML.
3. Support for multi-arm treatments -> Improved multi-arm ESS via stochastic matching.
4. Support for survival outcomes -> Use of data simulation from survival outcome models to implement stacked-ensemble for TE estimation in right-censored, time-to-event data.
5. Bootstrapped confidence interval (CI) estimation -> Honest estimation of CI by including entire (matching + TE estimation) pipeline in bootstrap loop.
6. Compatible with scikit-learn -> Maximum flexibility in using ML models by providing access to scikit-learn (and scikit-survival for survival) for propensity-score, outcome and meta-learner stages.
7. Full reproducibility of results --> Careful implementation of random number generation (RNG) seeding, including in scikit-learn models.

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API

Function	Brief description
estimate_te	Main pipeline – ensemble matching + meta‑learner
StochasticMatcher	1:1 nearest‑neighbor matcher (deterministic ↔ stochastic)
summarize_matching	Diagnostics: ESS, ASMD, variance ratios, overlap plots
load_data_lalonde	Copy of Lalonde job‑training dataset
load_data_tof	Simulated TOF dataset (survival or binary outcome)

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⚙️ Installation

pip install causalem

Optional dev extras:

pip install "causalem[dev]"

Minimum Python 3.9. Tested on macOS and Windows.

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Package Vignette

For a more detailed introduction to CausalEM, including the underlying math, see the package vignette [insert link later], available on arXiv.

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🚀 Quick Start

Two-arm Analysis

Load the necessary packages:

import numpy as np
import pandas as pd
from sklearn.ensemble import RandomForestClassifier
from sklearn.linear_model import LogisticRegression

from causalem import (
  estimate_te,
  load_data_tof,
  stochastic_match,
  summarize_matching
)

Load the ToF data with two treatment levels and binarized outcome:

X, t, y = load_data_tof(
  raw = False,
  treat_levels = ['PrP', 'SPS'],
  binarize_outcome=True,
)

Stochastic matching using propensity scores:

lr = LogisticRegression(solver="newton-cg", max_iter=1000)
lr.fit(X, t)
score = lr.predict_proba(X)[:, 1]
logit_score = np.log(score / (1 - score))

cluster = stochastic_match(
    treatment=t,
    score=logit_score,
    nsmp=10,
    scale=1.0,
    random_state=0,
)

diag = summarize_matching(
  cluster, X,
  treatment=t, plot=False
)
print("Combined Effective Sample Size (ESS):", diag.ess["combined"])
print("Absolute standardized mean difference (ASMD) by covariate:\n")
print(diag.summary)

TE estimation:

res = estimate_te(
    X,
    t,
    y,
    outcome_type="binary",
    niter=5,
    matching_scale=1.0,
    matching_is_stochastic=True,
    random_state_master=1,
)
print("Two-arm TE:", res["te"])

Multi-arm Analysis

Load data for multi-arm analysis:

df = load_data_tof(
  raw = True,
  binarize_outcome=True,
)
t_all = df["treatment"].to_numpy()
X_all = df[["age", "zscore"]].to_numpy()
y_all = df["outcome"].to_numpy()

Constructing propensity scores using multinomial logistic regression:

lr_multi = LogisticRegression(multi_class="multinomial", max_iter=1000)
lr_multi.fit(X_all, t_all)
proba = lr_multi.predict_proba(X_all)
ref = "PrP"
cols = [i for i, c in enumerate(lr_multi.classes_) if c != ref]
logit_multi = np.log(proba[:, cols] / (1 - proba[:, cols]))

Multi-arm stochastic matching:

cluster_multi = stochastic_match(
    treatment=t_all,
    score=logit_multi,
    nsmp=5,
    scale=1.0,
    ref_group=ref,
    random_state=0,
)
diag_multi = summarize_matching(
    cluster_multi, X_all, treatment=t_all, ref_group=ref, plot=False
)
print("Multi-arm ESS per draw:\n", diag_multi.ess["per_draw"])

Multi-arm TE estimation:

res_multi = estimate_te(
    X_all,
    t_all,
    y_all,
    outcome_type="binary",
    ref_group=ref,
    niter=5,
    matching_scale=1.0,
    matching_is_stochastic=True,
    random_state_master=1,
)
print("Multi-arm pairwise effects:\n", res_multi["pairwise"])

Confidence-Interval Calculation

Adding bootstrap CI to the two-arm analysis:

res_boot = estimate_te(
    X,
    t,
    y,
    outcome_type="binary",
    niter=5,
    nboot=200,
    matching_scale=1.0,
    matching_is_stochastic=True,
    random_state_master=1,
    random_state_boot=7,
)
print("Bootstrap CI:", res_boot["ci"])

Heterogeneous Ensemble

learners = [
    LogisticRegression(max_iter=1000),
    RandomForestClassifier(n_estimators=200, max_depth=3),
]
res_ensemble = estimate_te(
    X,
    t,
    y,
    outcome_type="binary",
    model_outcome=learners,
    niter=len(learners),
    do_stacking=True,
    matching_scale=1.0,
    matching_is_stochastic=True,
    random_state_master=42,
)
print("Ensemble TE:", res_ensemble["te"])

Stacking vs No-Stacking

# No-stacking: average per-iteration effects without appearance weights
res_ns = estimate_te(
    X,
    t,
    y,
    outcome_type="binary",
    niter=5,
    do_stacking=False,
    random_state_master=0,
)

# Stacking: meta-learner fit with appearance weights over the matched union
res_stack = estimate_te(
    X,
    t,
    y,
    outcome_type="binary",
    niter=5,
    do_stacking=True,
    random_state_master=0,
)

TE Estimation for Survival Outcomes

X_surv, t_surv, y_surv = load_data_tof(
  raw=False
  , treat_levels = ['SPS', 'PrP']
)
res_surv = estimate_te(
    X_surv,
    t_surv,
    y_surv,
    outcome_type="survival",
    niter=5,
    matching_scale=1.0,
    matching_is_stochastic=True,
    random_state_master=0,
)
print("Survival HR:", res_surv["te"])

License

This project is licensed under the terms of the MIT License.

Release Notes

0.6.2

• Exposed a new n_mc argument in estimate_te for specifying Monte‑Carlo draws per matched unit in survival analyses, replacing the previously fixed single draw.
• Clarified treatment‑effect estimands for stacking vs. no‑stacking modes, noting that stacked results are appearance‑weighted across the matched union.
• Documented appearance‑weighted meta‑learning and matched‑union survival contrasts.

0.6.1

• Corrected the version number in pyproject.toml file.

0.6.0

• Improved consistency of return data structure when do_stacking=False in multi-arm TE estimation.

0.5.4

• Added github action for publishing to PyPI

0.5.3

• First public release

0.5.1

• Edits to readme
• Added github action for publishing to (test) PyPI

0.5.0

• First test release