Quartiles, the 5-Number Summary, and Box-and-Whisker Plots

In this brief video, we introduce the concept of the quartiles for a data set. We provide two protocols to locate these values: the first is the by-hand method of locating the median for the upper- and lower-halves of the data, and the second is using percentiles and the L-locator method. After defining the quartiles and providing a means of calculating them by-hand, we introduce the 5-number summary: minimum, maximum, median & quartiles. Finally, we show how to use these five numbers to construct the box-&-whisker plot (also just called a boxplot) for a data set. We also elaborate on how the boxplot can be used to interpret the density of data in the intervals indicated by the boxplot.