Class Limits, Boundaries and Intervals
Class Limits
Class limits are the smallest and largest observations (data, events etc) in each class. Therefore, each class has two limits: a lower and upper.
Example:
| Class | Frequency |
| 200 – 299 | 12 |
| 300 – 399 | 19 |
| 400 – 499 | 6 |
| 500 – 599 | 2 |
| 600 – 699 | 11 |
| 700 – 799 | 7 |
| 800 – 899 | 3 |
| Total Frequency | 60 |
Using the frequency table above, what are the lower and upper class limits for the first three classes?
For the first class, 200 – 299
The lower class limit is 200
The upper class limit is 299
For the second class, 300 – 399
The lower class limit is 300
The upper class limit is 399
For the third class, 400 – 499
The lower class limit is 400
The upper class limit is 499
Class Boundaries
Class Boundaries are the midpoints between the upper class limit of a class and the lower class limit of the next class in the sequence. Therefore, each class has an upper and lower class boundary.
Example:
| Class | Frequency |
| 200 – 299 | 12 |
| 300 – 399 | 19 |
| 400 – 499 | 6 |
| 500 – 599 | 2 |
| 600 – 699 | 11 |
| 700 – 799 | 7 |
| 800 – 899 | 3 |
| Total Frequency | 60 |
Using the frequency table above, determine the class boundaries of the first three classes.
For the first class, 200 – 299
The lower class boundary is the midpoint between 199 and 200, that is 199.5
The upper class boundary is the midpoint between 299 and 300, that is 299.5
For the second class, 300 – 399
The lower class boundary is the midpoint between 299 and 300, that is 299.5
The upper class boundary is the midpoint between 399 and 400, that is 399.5
For the third class, 400 – 499
The lower class boundary is the midpoint between 399 and 400, that is 399.5
The upper class boundary is the midpoint between 499 and 500, that is 499.5
Class Intervals
Class interval is the difference between the upper and lower class boundaries of any class.
Example:
| Class | Frequency |
| 200 – 299 | 12 |
| 300 – 399 | 19 |
| 400 – 499 | 6 |
| 500 – 599 | 2 |
| 600 – 699 | 11 |
| 700 – 799 | 7 |
| 800 – 899 | 3 |
| Total Frequency | 60 |
Using the table above, determine the class intervals for the first class.
For the first class, 200 – 299
The class interval = Upper class boundary – lower class boundary
Upper class boundary = 299.5
Lower class boundary = 199.5
Therefore, the class interval = 299.5 – 199.5
= 100