The measures of dispersion is also called measure of variation.
The Range
The range is the simplest and most straight forward measure of dispersion. It is the difference between the maximum values in the date.
Example
Find the range in the table below
| Marks | 6-10 | 11-15 | 16-20 | 21-25 | 26-30 | |
| Frequency | 3 | 5 | 2 | 6 | 4 |
Solution
The maximum (highest) score = 30
The minimum (lowest) score = 6
= 24.
Mean Deviation
Examples:
Calculate the mean deviation for the set of data in table below
Age of SS2 students that won scholarship
| 8 | 10 | 14 | 18 | |||
| 4 | 3 | 5 | 8 |
Solution
Age of SS2 students that won scholarship
VARIANCE AND STANDARD DEVIATION
Example: The marks scored by Economics Students in their NECO Examination are presented in the table below. Calculate the variance and standard deviation.
| Marks | 10 | 20 | 30 | 40 | 50 | 60 |
| No of students (frequency) | 8 | 6 | 12 | 18 | 6 | 4 |
Questions
Marks scored by some students in an economics test are;
6 9 5 7 6 7 5 8 9 5
8 9 5 7 5 8 7 8 6 5
6 5 7 6 9 9 7 8 8 7
8 9 8 5 8 9 5 6 9 7
8 5 6 9 8 6 7 6 9 5
- Find the range of the grouped frequency table below.
| X | 1-10 | 11-20 | 21-30 | 31-40 | 41-50 | 51-60 | 61-70 | 71-80 |
| F | 4 | 6 | 9 | 12 | 9 | 5 | 4 | 1 |
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