> ## Documentation Index
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# atoti.stats.normal.ppf()

### atoti.stats.normal.ppf(point, /, \*, mean, standard\_deviation)

Percent point function for a normal distribution.

<Warning>
  This feature is [`experimental`](./atoti.experimental#atoti.experimental), its key is `"stats.normal.ppf"`.
</Warning>

Also called inverse cumulative distribution function.

The ppf is given by the formula

$$
\operatorname {{ppf}}(x) = \mu + \sigma \sqrt{{2}} \operatorname {{erf}} ^{{-1}}(2x-1)
$$

Where $\mu$ is the mean of the distribution, $\sigma$ is its standard deviation and $\operatorname {{erf}}^{{-1}}$ the inverse of the error function.

* **Parameters:**
  * **point** (*VariableMeasureConvertible*) – The point where the function is evaluated.
  * **mean** (*NumericMeasureConvertible*) – The mean value of the distribution.
  * **standard\_deviation** (*StrictlyPositiveNumber* *|* *VariableMeasureConvertible*) – The standard deviation of the distribution.
    Must be positive.
* **Return type:**
  MeasureDefinition

<Callout icon="link">
  **See also**:
  [Quantile function of a normal distribution](https://en.wikipedia.org/wiki/Normal_distribution#Quantile_function).
</Callout>