Building a cumulative frequency table
Running total: each row's cumulative is its frequency plus all previous frequencies.
Method. Add a column to the frequency table; cumulative frequency at each row = frequency at that row + cumulative at the previous row.
Worked. Heights of students:
| Height (cm) | Frequency | Cumulative |
|---|---|---|
| 4 | 4 | |
| 12 | 16 | |
| 14 | 30 | |
| 8 | 38 | |
| 2 | 40 |
The final cumulative equals the total frequency: .
Plot. Plot cumulative frequency against the UPPER class boundary:
- .
Also plot — nothing below the lowest boundary.
Curve. Join with a smooth curve (NOT straight lines between points). The result is an "S-shaped" curve rising from to the total.
- Cumulative = running total of frequencies.
- Plot at UPPER class boundary.
- Include at the start.
- Smooth curve, not straight segments.