M4.7.5 For the adult
Histograms with unequal widths
The heights of plants are grouped in classes of different widths. How can one chart show them fairly?
What this chapter teaches
When the classes of a histogram have different widths, the height of a bar is the frequency density, which is the frequency divided by the class width. The area of a bar is then the frequency. A wide bar can be low and still hold many values.
Three questions to ask
There is no one right wording. Listen for the idea.
- Why does a bar as tall as its frequency mislead when the classes have unequal widths?
- A bar is 20 wide and 1.5 high. How many values does it stand for?
- Why is the tallest bar of a histogram not always the class with most values?
After the chapter, the learner can
- Draw a histogram using frequency density
- Read frequencies from a histogram
What they copy into their notebook
Frequency density = frequency ÷ class width. The height of a bar is the density. The area of a bar is the frequency: width × height.