Cumulative frequency and histograms · Grade 9
In Grade 9 you learn: cumulative frequency graphs.
When data are grouped into classes, cumulative frequency (a running total) lets you estimate the median and quartiles from a graph. Histograms show grouped continuous data. The AREA of each bar is the frequency, so the classes can have different widths.
Key facts
- Cumulative frequency is the running total of the frequencies.
- Plot each cumulative frequency at the upper end of its class and join the points.
- Median ≈ the value at n/2 on the cumulative frequency axis. Q1 is at n/4 and Q3 at (3n)/4.
- Estimated mean of grouped data = Σ(f × midpoint) ÷ Σf.