alterlab-multilevel-models

name	alterlab-multilevel-models
description	Fits and reports mixed-effects / multilevel / hierarchical models for clustered, nested, longitudinal, and repeated-measures data — random intercepts and slopes, variance components and the ICC, cross-level interactions, and GLMMs (logistic/Poisson) — using statsmodels MixedLM and bambi (Bayesian on PyMC) in Python, or the field-standard R lme4 / glmmTMB / brms via Rscript. It enforces the reporting items reviews find under-reported: full fixed + random specification, centering, variance components + ICC, estimation method, assumption checks, model comparisons, and effect sizes. Use when data are grouped/nested (students in schools, repeated measures, panel/longitudinal) and the question concerns within- vs between-cluster variation. For general single-level regression prefer alterlab-statsmodels; for panel fixed effects used for causal identification prefer alterlab-causal-inference. Part of the AlterLab Academic Skills suite.
license	MIT
allowed-tools	Read Bash(python:*)
compatibility	Requires (declare in-session, no runtime install on Anthropic API): Python statsmodels>=0.14 (MixedLM), optionally bambi>=0.18 (Bayesian, on PyMC) — OR the field-standard R lme4>=2.0 (+ lmerTest for p-values), glmmTMB, brms, and performance (icc/r2) via Rscript. Runs locally via `uv run python` / `Rscript`; no API key.
metadata	{"skill-author":"AlterLab","version":"1.0.0","depends_on":"alterlab-statsmodels (single-level regression), alterlab-statistical-analysis, alterlab-causal-inference (panel FE for causal ID); audited by alterlab-ssci-inference-gate"}

Multilevel Models — Fit the Nesting, Report the Whole Model

Skill type: ANALYSIS MODULE. Correlated data (pupils in schools, repeated measures within people, panel waves) violate independence; a mixed-effects model partitions variance into levels. The value here is discipline, not a fit() call: methods reviews document a reporting crisis — models specified and reported inconsistently — so this skill enforces the reporting standard.

Core Mission

FITTING THE MODEL IS EASY; REPORTING IT COMPLETELY IS THE JOB.
STATE THE FULL FIXED + RANDOM STRUCTURE, THE ICC, THE ESTIMATION, THE CHECKS.

When to Use This Skill

• "I have students nested in schools / repeated measures / panel data — fit a multilevel model."
• "Random intercepts and slopes for [group]; what's the ICC?"
• "Multilevel logistic / Poisson (GLMM)."
• "How much variance is between groups vs within?"

Does NOT Trigger

The request is really about…	Route to	Why not this skill
Single-level / ordinary regression, no grouping	alterlab-statsmodels / alterlab-statistical-analysis	No random-effects structure needed.
Panel fixed effects for causal identification (DiD/within)	alterlab-causal-inference	FE-for-identification, not variance partitioning.
Latent variables / SEM / factor structure	alterlab-sem-psychometrics	Measurement model.
Whether the design/question even needs multilevel	alterlab-ssci-design-gate	Design routing.

Structure ≠ question

Having a multilevel data structure is not the same as having a question that requires multilevel analysis. If inference is at one level and clustering is only a nuisance, cluster-robust (sandwich) SEs may suffice; reach for a mixed model when the question concerns between-cluster variation (e.g. how much of the outcome varies across schools, or whether an effect varies by group). State which case you are in.

Verified calls (pinned)

Python — statsmodels MixedLM:

import statsmodels.formula.api  smf
m = smf.mixedlm(, data, groups=data[], re_formula=)   
res = m.fit(reml=)                    
res.summary(); res.cov_re