The class interval is the maximum possible value in the class less the maximum possible value in the class below. The second is equivalent to the minimum possible value in the class.

Because median is the mid of the class intervals. Therefore, it is a positional measurement. Hence, if the size of class interval increases or decreases then the middle position will also increase or decrease and thus median.

If, in a frequency distribution, the initial class interval is indeterminate at its beginning and/or the final class interval is indeterminate at its end, the distribution is said to possess "open ended" classes.