Index of coincidence
= Index of coincidence
{wiki=Index_of_coincidence}
The **Index of Coincidence (IC)** is a statistical measure used in cryptography and text analysis to assess the randomness of a text or a ciphertext. It quantifies how likely it is that two randomly selected letters from a string of text will be the same. This measure can help in cryptanalysis, particularly for identifying the type of simple substitution ciphers or for analyzing the properties of encrypted data.