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 stepdeviations
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
Continuous frequency distribution : Mean deviation about median Finding Median is a challenge here . Steps to find median : Arrange data in ascending order .
Cumulative frequency is derived Class in which median lies is identified .