More About Boxplots

What is a boxplot? A box plot is a chart tool used to quickly assess distributional properties of a sample. The so-called box-and-whiskers plot shows a clear indication of the quartiles of a sample as well of whether or not there are outliers.

There are different conventions, but the most common one indicate that the central box limits are determined by the quartiles \(Q_1\) and \(Q_3\). Inside of the central box there is line that represents the median (which is the same as \(Q_2\)). The whiskers are expressed in different ways, but one of the most common ways set the limit of the upper whisker as \(Q_3 + 1.5 \times IQR\), and the limit of the lower whisker as \(Q_1 – 1.5\times IQR\), where \(IQR\) is the intequartile range, that is defined as: \(IQR = Q_3 – Q_1\)