# Index of Coincidence

Index of Coincidence (IC) is the probability of two randomly selected characters being the same. This can be used to determine whether text is readable or random, with English text having an IC of around 0.066. IC can therefore be a sound method to automate frequency analysis. Index of Coincidence lives in the **Others** category of the `fx` menu.

## Parameter

| Parameter | Type   | Required | Default | Description                                            |
| --------- | ------ | -------- | ------- | ------------------------------------------------------ |
| Input     | string | yes      | —       | Value to transform. Previous step output or a literal. |

`Input` is the primary value (previous step output or a literal).

## Returned value

| Type     | Description                                        |
| -------- | -------------------------------------------------- |
| `number` | Result of the Index of Coincidence transformation. |

## Example

<details>
<summary>Run Index of Coincidence</summary>

Index of Coincidence (IC) is the probability of two randomly selected characters being the same. Adjust optional parameters when the defaults do not match your payload.

1. Set **Input** to the value to transform (previous step output or a literal).

2. Confirm **Output value** shows the transformed result.

</details>