Page 1 - LESSON NOTES

Statistics (Chapter 15)

Class 11

LESSON Notes.

Measure of Dispersion
The dispersion is the measure of variations in the values of the variable. It measures the degree of
scatteredness of the observation in a distribution around the central value.

Range
The measure of dispersion which is easiest to understand and easiest to calculate is the range.
Range is defined as the difference between two extreme observation of the distribution.
Range of distribution = Largest observation – Smallest observation.

Mean Deviation
Mean deviation for ungrouped data
For n observations x1, x2, x3,…, xn, the mean deviation about their mean [latex s=1]\bar { x }[/latex] is given
by

Mean deviation about their median M is given by

Mean deviation for discrete frequency distribution
Let the given data consist of discrete observations x1, x2, x3,……., xn occurring with frequencies f1, f2,
f3,……., fn respectively in case

Mean deviation about their Median M is given by