Relation To Standard Deviation
In order to use the MAD as a consistent estimator for the estimation of the standard deviation σ, one takes
where K is a constant scale factor, which depends on the distribution.
For normally distributed data K is taken to be 1/Φ−1(3/4) 1.4826, where Φ−1 is the inverse of the cumulative distribution function for the standard normal distribution, i.e., the quantile function. This is because the MAD is given by:
Therefore we must have that Φ(MAD/σ) − Φ(−MAD/σ) = 1/2. Since Φ(−MAD/σ) = 1 − Φ(MAD/σ) we have that MAD/σ = Φ−1(3/4) from which we obtain the scale factor K = 1/Φ−1(3/4).
Hence
In other words, the expectation of 1.4826 times the MAD for large samples of normally distributed Xi is approximately equal to the population standard deviation.
The factor results from the reciprocal of the normal inverse cumulative distribution function, evaluated at probability .
Read more about this topic: Median Absolute Deviation
Famous quotes containing the words relation to, relation and/or standard:
“Concord is just as idiotic as ever in relation to the spirits and their knockings. Most people here believe in a spiritual world ... in spirits which the very bullfrogs in our meadows would blackball. Their evil genius is seeing how low it can degrade them. The hooting of owls, the croaking of frogs, is celestial wisdom in comparison.”
—Henry David Thoreau (1817–1862)
“The proper study of mankind is man in his relation to his deity.”
—D.H. (David Herbert)
“Gentlemen, those confederate flags and our national standard are what has made this union great. In what other country could a man who fought against you be permitted to serve as judge over you, be permitted to run for reelection and bespeak your suffrage on Tuesday next at the poles.”
—Laurence Stallings (1894–1968)