M4.7.4 For the adult
Box plots
Two groups of plants have the same median height. How can I show in one small picture that one group is much more spread out?
What this chapter teaches
A box plot shows the smallest value, Q1, the median, Q3 and the largest value on one scale. For a short list, the quartiles are the medians of the lower and upper halves. Two groups are compared by their medians, for the middle, and their IQRs, for the spread.
Three questions to ask
There is no one right wording. Listen for the idea.
- How do you find Q1 and Q3 for a list of 11 values?
- What does a long box tell you compared with a short box?
- Two groups have the same median. How could box plots still show a difference?
After the chapter, the learner can
- Draw a box plot from five key values
- Compare two groups using box plots
What they copy into their notebook
Box plot: smallest, Q1, median, Q3, largest on one scale. The box is about half the data. Compare the medians for the middle, the IQRs for the spread.