How to teach reading and choosing data displays
Year 7 and Year 9 (ages 12 to 15)
Different data displays suit different kinds of data. This unit covers building and reading numerical displays like stem-and-leaf plots, describing their shape, centre and spread, and choosing the most suitable display for a given data set and question.
How to teach it
- Build a stem-and-leaf plot from a real numerical data set, splitting each value into a stem and a leaf.
- Describe the resulting shape (symmetric, skewed left/right, clustered) using the display, not just the raw numbers.
- Identify any outliers in the display and discuss whether they should influence a conclusion.
- Compare several display types (bar graph, stem-and-leaf, line graph, scatterplot) side by side on the same data where possible.
- Practise justifying a display choice: what type of data is it, and what question is the display meant to answer?
Common mistakes
- Building a stem-and-leaf plot with leaves out of order, making the shape harder to read at a glance.
- Describing a display's shape only in vague terms ('it's kind of spread out') instead of specific features (skewed, clustered, an outlier at X).
- Choosing a display type out of habit rather than because it suits the data and the question being asked.
- Treating an outlier as automatically an error, rather than investigating whether it is a genuine, meaningful value.
Frequently asked questions
What is a stem-and-leaf plot?
A stem-and-leaf plot splits each numerical value into a 'stem' (the leading digit(s)) and a 'leaf' (the last digit), letting you see both the individual values and the overall shape of the data at once.
How do you choose the right display for a data set?
Match the display to the data type and question: bar graphs and pictographs for categorical counts, stem-and-leaf plots or histograms for numerical spread, line graphs for change over time, and scatterplots for the relationship between two numerical variables.
What should you look for in a numerical data display?
Its shape (symmetric, skewed, clustered), its centre (roughly where the middle sits), its spread (how wide the values range), and any outliers (values far from the rest).
What year are numerical data displays and choosing the right display taught?
In the Australian Curriculum, creating and comparing numerical data displays like stem-and-leaf plots is a Year 7 skill (AC9M7ST02); choosing and justifying the right display for a data type extends to Year 9 (AC9M9ST04).
Practise with free worksheets
Printable worksheets with answer keys that are never wrong.