define-variables

# Define-Variables Skill ## Purpose Every observational study operationalizes abstract constructs (MASLD, CKD, emphysema, obesity, incidentaloma) into concrete rules against the available data dictionary. When that operationalization is invented ad-hoc from the dictionary alone, reviewers reject on construct validity regardless of downstream statistics. This skill forces a **literature-first** pass: each variable is mapped to a canonical guideline/consensus definition, cross-checked against prior operationalizations in comparable cohorts, then mapped to available DB variables. Ad-hoc deviations are flagged explicitly and justified, not hidden. Use it when: - a study question is known and variables are being selected - inclusion/exclusion criteria or phenotype definitions need citation backing - a data dictionary has ambiguous or derived variables (eGFR formula, BMI class, liver steatosis criteria, etc.) - a reviewer asked "why this cutoff?" - a retrospective audit reveals drifted definitions across projects in the same cohort Call after `/design-study`, before `/write-protocol`. ## Communication Rules - Communicate in the user's preferred language. - All variable names, guideline names, cutoffs in English. - Produce one artifact: `variable_operationalization.md` in the project root (or path the user specifies). ## Inputs 1. **Research question** (one sentence) 2. **Candidate variables** — exposure, outcome, key covariates, eligibility filters 3. **Data dictionary pat...