The class width is found by calculating the difference between the upper and lower boundaries of a class interval or the difference between the lower limits of two consecutive classes. The most common formula to find the class width is:
Class width=Maximum value−Minimum valueNumber of classes\text{Class width}=\frac{\text{Maximum value}-\text{Minimum value}}{\text{Number of classes}}Class width=Number of classesMaximum value−Minimum value
Here’s how to find it step by step:
- Identify the maximum and minimum values in the data set.
- Decide on the number of classes (intervals) you want to divide the data into.
- Subtract the minimum value from the maximum value to get the range.
- Divide the range by the number of classes.
- The result is the class width. If the result is not a whole number, round up to the nearest whole number for easier class intervals.
Alternatively, if working directly with class intervals, you can subtract the lower boundary of one class from the lower boundary of the next class to get the class width. Example: Given a range from 45 to 90 and 9 classes,
Class width=90−459=5\text{Class width}=\frac{90-45}{9}=5Class width=990−45=5
This means each class interval will have a width of 5 units. The class width is important for creating frequency distribution tables and histograms, as it helps determine the size of the intervals in which data is grouped.
