Unformatted text preview: es computed from any measure of central tendency;
i.e., the mean, median or mode, all the deviations are taken as
positive i.e., signs are ignored. According to Clark and
Schekade,
“Average deviation is the average amount scatter of the
items in a distribution from either the mean or the median,
ignoring the signs of the deviations”.
We usually compute mean deviation about any one of
the three averages mean, median or mode. Some times mode
may be ill defined and as such mean deviation is computed
from mean and median. Median is preferred as a choice
between mean and median. But in general practice and due to
wide applications of mean, the mean deviation is generally
computed from mean. M.D can be used to denote mean
deviation.
7.5.2 Coefficient of mean deviation:
Mean deviation calculated by any measure of central
tendency is an absolute measure. For the purpose of comparing
variation among different series, a relative mean deviation is
required. The relative mean deviation is obtained by dividing
the mean deviation by the average used for calculating mean
deviation.
149 Mean deviation
Mean or Median or Mode
If the result is desired in percentage, the coefficient of mean
Mean deviation
deviation =
× 100
Mean or Median or Mode
7.5.3 Computation of mean deviation – Individual Series :
1. Calculate the average mean, median or mode of the
series.
2. Take the deviations of items from average ignoring
signs and denote these deviations by D.
3. Compute the total of these deviations, i.e., Σ D
4. Divide this total obtained by the number of items.
∑ D
Symbolically: M.D. =
n
Example 6:
Calculate mean deviation from mean and median for the
following data:
100,150,200,250,360,490,500,600,671 also calculate coefficients of M.D.
Coefficient of mean deviation: = Solution:
Mean = x = ∑x
n = 3321
=369
9 Now arrange the data in ascending order
100, 150, 200, 250, 360, 490, 500, 600, 671 n + 1
Median = Value of item
2
th 9 + 1
= Value of item
2
= Value of 5th item
= 360
th 150 X D = x...
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 Winter '08
 Moshiri
 Business, Statistics

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