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Cohen's Kappa Formula:
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Cohen's Kappa (κ) is a statistical measure that calculates inter-rater agreement for qualitative (categorical) items. It measures the agreement between two raters beyond what would be expected by chance alone, making it more robust than simple percentage agreement.
The calculator uses the Cohen's Kappa formula:
Where:
Explanation: The formula subtracts the expected agreement from the observed agreement and normalizes it by the maximum possible improvement over chance.
Details: Cohen's Kappa is widely used in research, psychology, medicine, and social sciences to assess the reliability of categorical measurements, diagnostic tests, and classification systems between different observers or measurement tools.
Tips: Enter observed agreement and expected agreement as percentages (0-100%). The calculator automatically converts them to proportions and computes Cohen's Kappa. Values range from -1 (complete disagreement) to +1 (perfect agreement).
Q1: What do different Kappa values mean?
A: <0 = Poor agreement; 0-0.20 = Slight agreement; 0.21-0.40 = Fair agreement; 0.41-0.60 = Moderate agreement; 0.61-0.80 = Substantial agreement; 0.81-1.00 = Almost perfect agreement.
Q2: How is expected agreement calculated?
A: Expected agreement is calculated based on the marginal probabilities of each rater's classifications, representing the agreement that would occur by random chance.
Q3: When should Cohen's Kappa be used?
A: Use when assessing agreement between two raters on categorical data, especially when chance agreement could be substantial.
Q4: What are the limitations of Cohen's Kappa?
A: Kappa can be affected by prevalence and bias, and may not be appropriate for imbalanced data distributions or when there are more than two categories.
Q5: How does Kappa differ from percentage agreement?
A: Percentage agreement doesn't account for chance agreement, while Kappa provides a chance-corrected measure of agreement.