Data sets often include many measurements from each individual. For example, the following information might be collected from all students who completed a statistics course.
Student name | Age | Sex | Test mark(%) | Maths grade | Stats grade |
---|---|---|---|---|---|
John | 19 | Male | 76 | B | A |
Michelle | 20 | Female | 62 | B | C |
Alex | 18 | Male | 48 | Not enrolled | C |
Clare | 19 | Female | 68 | A | B |
... | ... | ... | ... | ... | ... |
Some measurements are numerical (age and marks in an internal test) and they can be examined with the graphical and numerical summaries that were described in earlier chapters. Other measurements (sex, maths grade and stats grade) do not have numerical values and are called categorical data. Different methods are required to display (and get information from) batches of categorical measurements.