Page 38 - 10-Math-6 BASIC STATISTICS

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Class Boundaries Frequency
10 ____ 20 2
20 ____ 30 5
30 ____ 40 9
40 ____ 50 6
50 ____ 60 4
60 ____ 70 1

6.4 Measures of Dispersion

Statistically, Dispersion means the spread or scatterness of
observations in a data set.
The spread or scatterness in a data set can be seen in two ways:
(i) The spread between two extreme observations in a
data set.
(ii) The spread of observations around an average say
their arithmetic mean.
The purpose of finding Dispersion is to study the behavior of
each unit of population around the average value. This also helps
in comparing two sets of data in more detail.
The measures that are used to determine the degree or extent
of variation in a data set are called Measures of Dispersion.
We shall discuss only some important absolute measures of
dispersion now.
(i) Range
Range measures the extent of variation between two extreme
observations of a data set. It is given by the formula:
Range = Xmax - Xmin = Xm - X0
where Xmax = Xm : the maximum, highest or largest observation.
Xmin = X0 : the minimum ,lowest or smallest observation.
The formula to find range for grouped continuous data is
given below:
Range = (Upper class boundary of last group) - (lower class boundary
of first group

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