Kappa
Kappa is a way to assess a system based on the degree of agreement in a measurement system, to see if it is more effective than guessing at the right answer (usually pass/fail decisions).
If you flipped a coin and you guessed heads or tails, you would be right about 50% of the time by chance
- Kappa = 0 means that you were equal to random chance (50%)
- Kappa < 0 means that you were worse than random chance (less than 50% correct)
- Kappa > 0 means that you were better than random chance (more than 50% correct)
- Kappa = 1 means that you were correct 100% of the time
The formula for calculating kappa is below…
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Where Po is the actual probability of occurrence, and Pe is expected probability of occurrence.
In the coin toss study, Po = 62 heads out of 100 = 0.62, and Pe = 0.50 (50% chance of heads)