What is the formula for calculating inter-rater reliability?

There isn’t just one formula for calculating inter-rater reliability. The right one depends on your data type (e.g., nominal data, ordinal data) and the number of raters.

  • Cohen’s kappa (κ) is commonly used for two raters
  • Fleiss’ kappa is typically used for three or more raters
  • The Intraclass Correlation Coefficient (ICC) is used for continuous data (interval or ratio). This is based on analysis of variance (ANOVA)

The most commonly used formula (for Cohen’s kappa) is:
\kappa = \dfrac{{{P}_o}-{{P}_e}}{{1}-{P_e}}
Po is the observed proportion of agreement, and Pe stands for the expected agreement by chance.

Related article: What Is Reliability? | Definition, Types & Examples

Reliability in research refers to how consistently a research method measures something. If you use the same method on the same group under the same conditions, you should get similar results each time. If the results vary significantly, the measurement may be unreliable or affected by bias or random error. Researchers use reliability to evaluate […]

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