Purpose: This paper introduces readers to the problem of measuring interrater agreement in observer variation studies. The most usual statistic to quote is the kappa coefficient which measures agreement having corrected for chance.
Method: The kappa coefficient for measuring agreement between two observers is introduced. Some pointers are given to determining sample size estimation.
Results: Some properties of the kappa coefficient are illustrated by taking examples from the author's teaching experiences.
Conclusion: The kappa coefficient is recommended for measuring agreement in observer variation studies.