alterlab-sem-psychometrics

name	alterlab-sem-psychometrics
description	Fits and evaluates measurement models — confirmatory factor analysis, full structural equation models, exploratory factor analysis, item response theory, and multi-group measurement invariance — using the verified Python stack: semopy (model syntax =~ / ~ / ~~, Model.fit, inspect(std_est=True), calc_stats for CFI/TLI/RMSEA), factor_analyzer (EFA, KMO, Bartlett, ConfirmatoryFactorAnalyzer), and pingouin/girth, computing McDonald's omega from standardized loadings and judging fit against Hu & Bentler cutoffs. Use when the request mentions confirmatory factor analysis, structural equation modeling, a latent variable or construct model, factor loadings, IRT, or measurement invariance across groups. For deciding whether a scale is trustworthy at all prefer alterlab-ssci-measurement-gate; for plain regression prefer alterlab-statistical-analysis. 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): semopy>=2.3, factor_analyzer>=0.5, pingouin>=0.5, optionally girth (IRT) (pip). SRMR and omega are not returned by semopy — compute omega with the bundled script; IRT beyond 2PL is often better in R mirt. Runs locally via `uv run python`; no API key.
metadata	{"skill-author":"AlterLab","version":"1.0.0","depends_on":"alterlab-ssci-measurement-gate (gates whether to trust the scale), alterlab-statistical-analysis; audited by alterlab-ssci-inference-gate"}

SEM & Psychometrics — Fit the Measurement Model, Judge It Honestly

Skill type: ANALYSIS MODULE. Fits CFA / SEM / EFA / IRT and tests measurement invariance. The discipline: report fit against real cutoffs, report reliability with omega (not alpha alone), and establish invariance before comparing groups. Whether the scale should be trusted at all is the upstream call of alterlab-ssci-measurement-gate.

Core Mission

A MEASUREMENT MODEL IS ONLY DONE WHEN FIT, RELIABILITY (OMEGA), AND INVARIANCE ARE ALL REPORTED.

When to Use This Skill

• "Run a confirmatory factor analysis on my scale."
• "Fit a structural equation model / a latent-variable path model."
• "Do an exploratory factor analysis — how many factors?"
• "Fit an IRT model / get item difficulty and discrimination."
• "Test measurement invariance across countries before I compare latent means."

Does NOT Trigger

The request is really about…	Route to	Why not this skill
Whether the scale is valid/trustworthy at all (reliability≠validity discipline)	alterlab-ssci-measurement-gate	Gate decision, upstream of fitting.
Writing / wording the questionnaire items	alterlab-survey-design	Instrument construction.
Plain regression / descriptive stats	alterlab-statistical-analysis	No latent structure.
A causal treatment-effect estimate	alterlab-causal-inference	Different problem.

Verified calls (pinned)

CFA / SEM — semopy (v2.3):

from semopy import Model, calc_stats
desc = """
# measurement model
Trust =~ q1 + q2 + q3
Efficacy =~ q4 + q5 + q6
# structural path
Trust ~ Efficacy
"""
m = Model(desc); m.fit(data)          # obj='MLW' default; 'FIML' for missing
est = m.inspect(std_est=True)          # standardized loadings for omega
stats = calc_stats(m)                  # DataFrame: chi2, CFI, TLI, RMSEA, AIC, BIC ...