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Frequency polygons and histograms are used to display continuous grouped data. Histograms with unequal class widths are a Higher-tier topic and are a favourite of Edexcel examiners.
| Term | Definition |
|---|---|
| Frequency polygon | A line graph plotted at the midpoints of class intervals against frequency |
| Histogram | A bar chart for continuous data where the area of each bar represents the frequency |
| Frequency density | Frequency ÷ class width; used as the vertical axis in histograms with unequal class widths |
| Class width | Upper class boundary − lower class boundary |
A frequency polygon is drawn by plotting points at the midpoint of each class interval against the frequency, then joining the points with straight lines.
Worked Example:
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