Here’s How to Analyze a Box Plot

A box plot is a data visualization technique for analyzing the distribution and patterns of numerical data points. Understanding data visualization graphs is not easy for everyone. So if you want to know how to analyze a box plot, this article is for you. In this article, I will take you through a guide on analyzing a box plot.

Structure of a Blox Plot

structures of a box plot

The box portion of a box plot contains three lines:

  1. The first line in the top represents quartile 3 of the data points;
  2. The second line in the middle represents the median value of the data points;
  3. The third line in the box plot represents quartile 1 of the data points;
  4. The two horizontal lines below and above the box are whisker lines;

I hope you have understood the structure of a box plot. The section below will introduce how to analyze a box plot.

Here’s How to Analyze a Box Plot

The image below shows three box plots visualizing how the number of bank accounts affects your credit scores.

how to analyze a box plot: box blot
Source: Credit Score Classification

In the above image, the green box plot shows the distribution of the number of bank accounts of credit card customers. In this graph:

  1. q1 = 2 (means 25% of the data lies below this point)
  2. median = 3 (means 50% of the data lies below this point)
  3. q3 = 5 (means 75% of the data lies below this point)
  4. the upper whisker represents the maximum value (9), and the lower whisker represents the minimum value (0)
  5. The green point above the upper whisker is an outlier representing 10 bank accounts and still have a good credit score

When the median is in the middle of the box plot, it represents standard distribution. When the median is closer to quartile 1 (as shown in the green box plot) it represents a positively skewed distribution. And when the median is closer to quartile 3 (as shown in the red box plot) it represents a negatively skewed distribution.

Summary

So below are some takeaways on how to analyze a box plot:

  1. The first line in the top represents quartile 3 of the data points, which means that 75% of the data lies below this point;
  2. The second line in the middle represents the median value of the data points, which means that 50% of the data lies below this point;
  3. The third line in the box plot represents quartile 1 of the data points, which means that 25% of the data lies below this point;
  4. The two horizontal lines below and above the box are whisker lines, the above whisker represents the maximum value, and the lower whisker represents the minimum value.
  5. Any point above the upper whisker line and below the lower whisker line is an outlier.

I hope you liked this article on how to analyze a box plot. Feel free to ask valuable questions in the comments section below.

Aman Kharwal
Aman Kharwal

I'm a writer and data scientist on a mission to educate others about the incredible power of data📈.

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