Understanding the Fundamentals of Statistics with Box Plots

A box and whisker plot — also called a box plot — displays the five-number summary of a set of data. The five-number summary is the minimum, first quartile, median, third quartile, and maximum.

In a box plot, we draw a box from the first quartile to the third quartile. A vertical line goes through the box at the median. The whiskers go from each quartile to the minimum or maximum.

Different parts of a boxplot | Image: Michael Galarnyk

Basic Terminology

• Data are any collection of observations or measurements. Data can be quantitative (numerical) or qualitative (categorical).
• A variable is any characteristic or attribute that can be measured or observed. Variables can be quantitative (e.g., age, weight) or qualitative (e.g., gender, color).
• A distribution is a summary of how frequently each value appears in a dataset. It can be described using measures of central tendency and spread.
• Measures of central tendency describe the typical or central value of a dataset. The mean and median are the two most commonly used measures of central tendency. The mean is the average of all values in the dataset…