Cumulative frequency tables
Running total. Plot at the UPPER BOUND.
Cumulative frequency is a running total β the count of values up to and including a given point.
Worked example. Times: β (5), β (12), β (8), β (5). Total .
Cumulative table:
| Time | Cumulative freq |
|---|---|
| 5 | |
| 17 | |
| 25 | |
| 30 |
KEY RULE. Plot cumulative frequency at the UPPER BOUND of each class β NOT the midpoint, NOT the lower bound.
Why? Because "cumulative frequency at " means "how many had time UP TO 20". The class β contributes its full 12 to that count.
Edexcel tip. Always start the curve at if there are no values below the first class β otherwise the curve doesn't pass through the origin.
- Running total.
- Plot at upper bound.
- Start curve at zero where appropriate.
- Final cumulative = total .