Which statement best describes the interpretation of the kappa statistic?

• A. It measures the proportion of observed agreement that is due to chance.
• B. It indicates the total proportion of all agreements, both positive and negative.
• C. It indicates how much better than chance the observed agreement is.
• D. It is identical to the overall percent agreement.

Answer: (C)

Kappa measures agreement beyond what would be expected by chance. It takes the observed agreement between raters and removes the portion that could occur just by guessing, then scales that difference relative to the maximum possible improvement over chance. In practical terms, it uses Po for observed agreement and Pe for the expected agreement by chance, with the formula kappa = (Po − Pe) / (1 − Pe). If Po is close to Pe, kappa is near zero, meaning little agreement beyond chance; if Po is much larger than Pe, kappa is higher, showing stronger agreement beyond chance; a negative value indicates agreement worse than what would be expected by chance. This is why describing it as how much better than chance the observed agreement is best captures what kappa represents. The other statements describe the total observed agreement, or agreement that could occur by chance alone, rather than the adjusted, beyond-chance agreement that kappa quantifies.