Cumulative Frequency
A running total of frequencies, where the cumulative frequency for a class is the sum of the frequency of that class and all preceding classes. Used to find medians, quartiles, and percentiles through interpolation in grouped data.
Real World
Ofqual plots cumulative frequency curves of A-level grade boundaries each summer to determine what percentage of students scored below each threshold nationwide.
Exam Focus
Plot cumulative frequency against upper class boundaries, not midpoints — this is the most common error on the paper.
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