Coefficient of Coincidence Calculator

Formula

The formula to calculate the Coefficient of Coincidence (COC) is:

\[ COC = \frac{\sum (f_{i} (f_{i} - 1))}{N (N - 1)} \]

Where:

Coefficient of Coincidence (COC): A statistical measure used in cryptanalysis to determine the likelihood of two random variables coinciding.
Frequency of Occurrence (f_i): The number of times a particular variable occurs in the data set.
Total Number of Observations (N): The total number of data points in the data set.
Significance: A higher COC indicates a higher probability of coincidence, suggesting a stronger correlation between the variables.

Let's say the frequencies are 5, 3, and 2, and the total number of observations (N) is 10. Using the formula:

\[ COC = \frac{(5 \times 4) + (3 \times 2) + (2 \times 1)}{10 \times 9} = \frac{20 + 6 + 2}{90} = \frac{28}{90} = 0.3111 \]

So, the Coefficient of Coincidence (COC) is 0.3111.