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