Statistics / IGCSE / AI

Histograms and Frequency Density

Represent grouped continuous data using frequency density so that bar area represents frequency.

Frequency density

\[\text{frequency density}=\frac{\text{frequency}}{\text{class width}}.\]

For unequal class widths, the bar heights must be frequency densities, not frequencies.

class intervalsdensity
In a histogram, bar area is proportional to frequency, so height is frequency density.

Common mistake

Do not leave gaps between histogram bars for continuous data, and do not use frequency as height when class widths are unequal.