3. Objectives
At the end of this presentation you should be able
to :
- Define the standards deviation
- List the merit and demerit of obtaining
standards deviation
- Calculate the variance and standard deviation
4. Standard Deviation
- Standard deviation measures the dispersion of data.
- It shows the average absolute distance of each point from
the mean
- The greater the value of standard deviation, the further the
data tend to be dispersed from the mean.
5. Merits of Standard Deviation
1- It is the most reliable measure of dispersion
2- It is most widely used measure of dispersion or
variability
3- Its computation is based on all the observations.
6. Demerits of Standard Deviation
1- It is relatively difficult to calculate and understand.
2- It cannot be used for comparing the dispersion of two, or more
series given in different units.
3- It is affected very much by the extreme values
7. Formula
Standard deviation has a symbol (Ο) if the data represent a population and (s) if
the data represent a sample
Ο =
(πβ π ) π
π
s =
(πβ π ) π
πβπ
Population
Sample
10. Summary
- Standard deviation measure the dispersion of data.
- It is the most reliable
- The greater the value of standard deviation, the further the
data tend to be dispersed from the mean.