Concordance Study

Definition: A *concordance study* evaluates the degree of agreement between two or more observers, diagnostic tools, or treatment decisions when applied to the same cases or data.

• Objective: Assess consistency between different evaluators or systems.
• Metrics commonly used:
  • Cohen’s kappa or Fleiss' kappa (for categorical variables)
  • Intraclass Correlation Coefficient (ICC) (for continuous variables)
  • Bland-Altman plots
  • Percentage agreement
• Typical design: Cross-sectional or retrospective analysis using shared clinical data or case vignettes.

• Inter-rater reliability (e.g., between radiologists)
• Comparing diagnostic or management decisions across clinical specialties
• Assessing guideline adherence across practitioners

A concordance study may analyze how often neurosurgeons and chiropractors agree on diagnosis and management of patients with low back pain, measuring the rate of agreement across a shared set of patient cases.