Business Statistics

Chapter 4 | Measures of Dispersion 135

m, that is, mean 1 standard deviation covers 68.27% of the items in a data set.

m, that is, mean 2 standard deviation covers 95.45% of the items in a data set.

m, that is, mean 3 standard deviation covers 99.73 of the items in a data set.

Figure 4.11 explains the area under the normal curve.

4.6 EMPIRICAL RELATIONSHIP BETWEEN MEASURES OF

DISPERSION

In the case of a symmetrical distribution, the empirical relationship between the various measures of

dispersion is given by:

1. Quartile deviation

2

3

=

Standard deviation, that is,

2

QD

3

= 

2. Mean absolute deviation

4

5

=

Standard deviation, that is, ...