Question

Why don’t you indicate the 4^th quartile on a box plot?

Does the distance from the 1^st quartile to the 2^nd quartile indicate the number of observation in that part of the boxplot? If not, why?

Answer 1

A box plot is used to represent the statistical data. Mainly it is used to get view of the 5 point summary, that inter quartile ranges, first and third quartile and the median. The fourth quartile in general represents the 100th percentile, that is the data point which is last in data. If we include that in box plots than the concept of outliers is wasted. And some times due to outliers that IQR becomes very large which is not so in general. So in order to get data not distorted due to outliers the 4th quartile is not used on box plot.

The distance between first and 3rd quartile indicates the distance in which 25% of the data points lie. Thus in a sense we can say that yes it gives us information about the number of data points that lie in that region.