A histogram can be used to represent grouped continuous data.

The area of each bar is proportional to the frequency in each class, which can lead to uneven widths of bars representing unequal class intervals.

The \(\y\)-axis is labelled frequency density.

\(\text{frequency density} × \text{class width} = \text{frequency} \)

A frequency polygon is formed by joining the middle of the top of each bar in a histogram.