|Class 11 Maths Statistics||Shortcut method|
Shortcut method for calculating mean deviation about mean
We take an assumed mean which is in the middle or just close to it in the data. Then deviations of the observations (or mid-points of classes) are taken from the assumed mean. This is nothing but the shifting of origin from zero to the assumed mean on the number line.
If there is a common factor of all the deviations, we divide them by this common factor to further simplify the deviations. These are known as step-deviations
The deviations and step-deviations reduce the size of the observations, so that the
computations viz. multiplication, etc., become simpler. Let, the new variable be denoted by d =(xi –a)/h where ‘a’ is the assumed mean and h is the common factor. Then, the mean x by step-deviation method is given by