# MedianDeviation MedianDeviation[data]

gives the median absolute deviation from the median of the elements in data.

# Details  • MedianDeviation is also known as MAD.
• MedianDeviation is a robust measure of dispersion, which means it is not very sensitive to outliers.
• For a vector data, {x1,x2,,xn}, the median deviation is given by the median of the vector {x1 ,,xn }, where is the median of data.
• • For matrix data, the median deviation is computed for each column vector with MedianDeviation[{{x1,y1,},{x2,y2,},}] equivalent to {MedianDeviation[{x1,x2,}],MedianDeviation[{y1,y2,}],}. »
• • For array data, the median deviation is equivalent to ArrayReduce[MedianDeviation,data,1]. »
• • MedianDeviation handles both numerical and symbolic data.
• The data can have the following additional forms and interpretations:
•  Association the values (the keys are ignored) » SparseArray as an array, equivalent to Normal[data] » QuantityArray quantities as an array » WeightedData based on the underlying EmpiricalDistribution » EventData based on the underlying SurvivalDistribution » TimeSeries, TemporalData, … vector or array of values (the time stamps ignored) » Image,Image3D RGB channel's values or grayscale intensity value » Audio amplitude values of all channels »

# Examples

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## Basic Examples(2)

MedianDeviation of a list:

MedianDeviation of columns of a matrix:

## Scope(13)

### Basic Uses(6)

Exact input yields exact output:

Approximate input yields approximate output:

Find the median deviation of WeightedData:

Find the median deviation of EventData:

Find the median deviation of TimeSeries:

The median deviation depends only on the values:

Find the median deviation of data involving quantities:

### Array Data(5)

MedianDeviation for a matrix works columnwise:

MedianDeviation for a tensor gives the columnwise median deviation at the first level:

Works with large arrays:

When the input is an Association, median deviation works on its values:

SparseArray data can be used just like dense arrays:

Find the median deviation of a QuantityArray:

### Image and Audio Data(2)

Channelwise median deviation value of an RGB image:

Median deviation value of a grayscale image:

On audio objects, MedianDeviation works channelwise:

## Applications(4)

Obtain a robust estimate of dispersion when extreme values are present:

Measures based on the Mean are heavily influenced by extreme values:

Identify periods of high volatility in stock data using a five-year moving median deviation:

Compute median deviations for slices of a collection of paths of a random process:

Choose a few slice times:

Plot median deviations over these paths:

Find the median deviation of the heights for the children in a class:

Plot the median deviation respective of the median:

## Properties & Relations(2)

MedianDeviation is the Median of absolute deviations from the Median:

For large uniform datasets, MedianDeviation and MeanDeviation are nearly the same:

## Possible Issues(1)

MedianDeviation requires real numeric values: ## Neat Examples(1)

Ratio of MedianDeviation to MeanDeviation for increasing sample size: