Chapter 25: Statistics: spread, grouped data and correlation
The chapter problem
Travel times
A school records the travel time, in minutes, for 20 pupils:
12, 14, 15, 16, 17, 18, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 29, 31, 35, 42
First contact: without calculating, predict whether the middle half of these times lies in a narrow or wide interval. Which value might make the data look less typical?
By the end of this chapter
You will be able to:
- find and interpret the median, quartiles and interquartile range;
- draw and read box plots and cumulative frequency graphs;
- use class width and frequency density to draw and interpret histograms;
- draw scatter graphs and describe correlation, including its limits;
- compare distributions using suitable measures and identify possible outliers.
Roadmap
- 25.1 Quartiles, interquartile range and box plots
- 25.2 Cumulative frequency
- 25.3 Histograms
- 25.4 Scatter graphs and correlation
- 25.5 Comparing distributions and outliers
- Review
Your turn to connect it
Where might you or someone you know compare typical values or variation, such as journey times, waiting times, or sports results? Write one example and name the measure that could help.