KS4 / GCSE · Mathematics — Higher
Cumulative Frequency
What is it
Cumulative frequency is the running total of frequencies up to a certain point, plotted as a graph to estimate the median, quartiles, and interquartile range of grouped data.
Why it matters
Cumulative frequency graphs let you estimate statistics like the median from data that's too grouped to calculate an exact answer from — a genuinely useful technique for working with real, imperfect data.
Exam tip
Always plot cumulative frequency against the upper boundary of each class interval, not the midpoint — using the midpoint instead of the upper boundary is a very common and easily avoidable error.
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