Histograms with Unequal Class Widths

Frequency Density

$\text{Frequency density} = \frac{\text{Frequency}}{\text{Class width}}$

$\text{Frequency} = \text{Frequency density} \times \text{Class width}$

Why Frequency Density?

With unequal class widths, using raw frequency would misrepresent the data. Frequency density ensures the area of each bar represents the frequency.

Drawing a Histogram

1. Calculate class widths.
2. Calculate frequency density for each class.
3. Draw bars with correct widths and heights (frequency density).
4. No gaps between bars (continuous data).

Reading a Histogram

Frequency = area of bar = width × height (frequency density).