What is a Box Plot?

The idea of box plot was presented by John Tukey in 1970. He wrote about it in his book “Exploratory Data Analysis” in 1977. Box plot is also known as a whisker plot, box-and-whisker plot, or simply a box-and whisker diagram. Box plot is a graphical representation of the distribution of a dataset. It displays key summary statistics such as the median, quartiles, and potential outliers in a concise and visual manner. By using Box plot you can provide a summary of the distribution, identify potential and compare different datasets in a compact and visual manner.

Elements of Box Plot

A box plot gives a five-number summary of a set of data which is-

• Minimum – It is the minimum value in the dataset excluding the outliers.
• First Quartile (Q1) – 25% of the data lies below the First (lower) Quartile.
• Median (Q2) – It is the mid-point of the dataset. Half of the values lie below it and half above.
• Third Quartile (Q3) – 75% of the data lies below the Third (Upper) Quartile.
• Maximum – It is the maximum value in the dataset excluding the outliers.

Note: The box plot shown in the above diagram is a perfect plot with no skewness. The plots can have skewness and the median might not be at the center of the box.

The area inside the box (50% of the data) is known as the Inter Quartile Range. The IQR is calculated as –

IQR = Q3-Q1

Outlies are the data points below and above the lower and upper limit. The lower and upper limit is calculated as – 

Lower Limit = Q1 - 1.5*IQR
Upper Limit = Q3 + 1.5*IQR

The values below and above these limits are considered outliers and the minimum and maximum values are calculated from the points which lie under the lower and upper limit.

Box Plot is a graphical method to visualize data distribution for gaining insights and making informed decisions. Box plot is a type of chart that depicts a group of numerical data through their quartiles.

In this article, we are going to discuss components of a box plot, how to create a box plot, uses of a Box Plot, and how to compare box plots.