Brainlag PlusCumulative frequency graphs, the median and interquartile range, box plots for comparing data, and histograms with frequency density.
Cumulative frequency
Cumulative frequency is a running total.
Plot each running total at the top of its class (the upper class boundary), start at zero at the bottom of the first class, and join the points with a smooth curve.
With 60 values, read across from 30 for the median, from 15 for the lower quartile and from 45 for the upper quartile. Here the median is about 25 minutes and the quartiles are about 18 and 32. The interquartile range = upper quartile − lower quartile: the spread of the middle half of the data, which an extreme value does not affect. Here it is about 32 − 18 = 14 minutes.
The rest of this lesson and its 8 practice questions are in Plus.
Screen 1 of 4, free to read.
- 8 exam-style questions, marked as you go, each with a worked solution
- Anything you get wrong is saved to your flashcards