Side-by-side boxplot

A side-by-side boxplot puts one boxplot per group along the same axis, so a difference in center reads as a shift and a difference in spread reads as a wider or narrower box. For example, if class A has median 78 with $Q_1 = 70$ (the first quartile) and $Q_3 = 84$ (the third quartile), while class B has median 85 with $Q_1 = 81$ and $Q_3 = 89$, then B sits 7 points higher with a smaller interquartile range (IQR) of $89 - 81 = 8$ against A's $84 - 70 = 14$. This site computes quartiles with the median-excluded (TI-84) rule. Because each box is built from only five numbers, a side-by-side boxplot can hide a gap, a cluster, or a second peak that a dotplot would show.