Calculation of Class Boundaries
Calculation of class boundaries for three class intervals can be illustrated with the help of following figure. The figure shows two methods for calculating the class boundaries. In the first method, class boundaries are calculated by adding the upper class limit of upper class to the lower class limit of next class divided by 2.
The second method shows that in case of equal size class interval, calculate class boundaries by adding the upper class limit of upper class to the lower class limit of next class divided by 2. Now subtract upper class limit of upper class from the number obtained as shown in the figure above. The figure shows that we get 0.5 after this calculation, which can be used to obtain class boundaries by subtracting it from the lower limits of all class intervals and adding it to the upper limits of all class intervals.
Calculation of Middle Class or Mid. Class
Each interval of frequency distribution is represented by the central value of the interval called the mid point of the interval. Mid. class can be calculated by adding the lower and upper class boundaries or by adding the lower and upper class limits and dividing by 2.