What does Kappa measure in a statistical context?

Kappa is a statistical measure that assesses the level of agreement or reliability between two observers or raters when categorizing items into discrete categories. It accounts for the agreement occurring by chance, providing a more accurate reflection of how much the observers agree beyond what would be expected if their assessments were made randomly.

This measure is particularly useful in fields where subjective judgment is involved, such as in medical diagnoses or assessments. The value of Kappa can range from -1 to 1, where values closer to 1 indicate almost perfect agreement, values around 0 suggest no agreement beyond chance, and negative values indicate less agreement than would be expected by chance alone.

In contexts where different observers are evaluating the same set of data or subjects, Kappa serves as a robust metric for understanding the consistency and reliability of those evaluations, making it pivotal in ensuring that assessments are standardized and reliable across different individuals.