| 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)
est = m.inspect(std_est=True)
stats = calc_stats(m)
