The answer is class intervals. A big set of data are grouped into different classes to get a hint of the distribution, and the range of such class of data is known as the Class Interval. In other words, these are range of scores in a group frequency distribution. Class intervals are commonly equal in width and are mutually exclusive. The middle of an interval is called a class mark and the ends of a class interval are called class limits. To calculate the class interval, divide the range by the number of classes.