1. What is Cohen's Kappa?

Cohen's Kappa (κ) is a statistical measure that calculates inter-rater agreement for categorical items. It accounts for the possibility of agreement occurring by chance, providing a more robust measure than simple percent agreement.

2. How Does the Calculator Work?

The calculator uses Cohen's Kappa formula:

Where:

• \( P_o \) — Observed agreement proportion (0-1)
• \( P_e \) — Expected agreement proportion by chance (0-1)
• \( \kappa \) — Cohen's Kappa coefficient (unitless)

Explanation: The formula subtracts the expected chance agreement from the observed agreement and normalizes it by the maximum possible improvement over chance.

3. Importance of Kappa Calculation

Details: Cohen's Kappa is crucial for assessing reliability in various fields including medical diagnosis, psychological testing, content analysis, and any situation requiring inter-rater reliability measurement.

4. Using the Calculator

Tips: Enter both Po and Pe as proportions between 0 and 1. Pe must be less than 1. Values closer to 1 indicate stronger agreement beyond chance.

5. Frequently Asked Questions (FAQ)

Q1: What do different kappa values mean?
A: κ ≤ 0 = No agreement, 0.01-0.20 = Slight, 0.21-0.40 = Fair, 0.41-0.60 = Moderate, 0.61-0.80 = Substantial, 0.81-1.00 = Almost perfect agreement.

Q2: When should I use Cohen's Kappa?
A: Use when you have two raters and categorical data. For more than two raters, consider Fleiss' kappa or other measures.

Q3: What are the limitations of Cohen's Kappa?
A: It can be affected by prevalence and bias. High agreement on rare categories may yield low kappa values (prevalence problem).

Q4: How do I calculate Po and Pe from raw data?
A: Po is the proportion of items where both raters agree. Pe is calculated from the marginal probabilities of each rater's classifications.

Q5: Can kappa be negative?
A: Yes, negative values indicate agreement worse than chance, suggesting systematic disagreement between raters.