Explain interrater reliability and one common statistic used to assess it.

• A. Measures consistency over time.
• B. Assesses predictive validity.
• C. Assesses agreement between observers; commonly Cohen's kappa or ICC.
• D. Measures content validity.

Answer: (C)

Interrater reliability is about how consistently different observers rate or code the same thing. It judges whether the measure yields similar results across raters, which is crucial for objectivity in things like behavioral coding or diagnostic ratings. A common statistic to assess this is Cohen's kappa, used for categorical ratings. It looks at how much agreement there is beyond what would be expected by chance, giving a value that reflects the strength of agreement. For continuous or ordinal ratings, the Intraclass Correlation Coefficient (ICC) is frequently used to quantify how much of the total variation comes from differences between subjects versus differences between raters; a higher ICC indicates better agreement among raters. This concept differs from consistency over time (test-retest reliability), predictive validity (how well a measure predicts an outcome), or content validity (whether the measure covers the relevant domain).