# Outliers¶

Simple outlier detection by comparing distances between instances.

## Signals¶

**Inputs**:

**Data**A data set

**Distances**A distance matrix

**Outputs**:

**Outliers**A data set containing instances scored as outliers

**Inliers**A data set containing instances not scored as outliers

## Description¶

The **Outliers** widget applies one of the two methods for outlier
detection. Both methods apply classification to the data set, one with
SVM (multiple kernels) and the other with elliptical envelope.
*One-class SVM with non-linear kernels (RBF)* performs well with
non-Gaussian distributions, while *Covariance estimator* works only for
data with Gaussian distribution.

- Information on the input data, number of inliers and outliers based on the selected model.
- Select the
*Outlier detection method*:**One class SVM with non-linear kernel (RBF)**: classifies data as similar or different from the core class**Nu**is a parameter for the upper bound on the fraction of training errors and a lower bound of the fraction of support vectors**Kernel coefficient**is a gamma parameter, which specifies how much influence a single data instance has

**Covariance estimator**: fits ellipsis to central points with Mahalanobis distance metric**Contamination**is the proportion of outliers in the data set**Support fraction**specifies the proportion of points included in the estimate

- Produce a report.
- Click
*Detect outliers*to output the data.

## Example¶

Below, is a simple example of how to use this widget. We used the *Iris*
data set to detect the outliers. We chose the *one class SVM with
non-linear kernel (RBF)* method, with Nu set at 20% (less training
errors, more support vectors). Then we observed the outliers in the
Data Table widget, while we sent the inliers to the Scatter
Plot.