Bar chart: comparing separate categories
Number of pets owned by each type in a class survey.
Bar charts are best when comparing separate, unrelated categories.
Year 8
Choose the most appropriate graph for a data set
Compare data representations critically and select the clearest statistical model for a given data set, justifying the choice.
Lesson overview
Statistics and data
Different data needs different graphs. Bar charts compare separate categories. Pie charts show how a whole splits into parts. Line graphs show how something changes over time. Scatter graphs show whether two different quantities are linked. Choosing the right graph makes data much easier to read -- the wrong choice can hide the pattern or mislead the reader.
Line graph: change over time
A town's average temperature recorded each month.
Line graphs are best for continuous data that changes over time.
Scatter graph: are two things linked?
Hours of sleep and reaction time for a group of athletes.
Scatter graphs test whether two different measurements are related.
Worked example
A shop wants to show how its total sales split between departments last month. Which graph fits best?
Total sales split into departments (parts of one whole)
One month, one total
Pie chart
Shows how the whole splits into parts
- Ask: is this comparing separate categories, showing change over time, showing parts of a whole, or checking a link between two things?
- The sales split into departments -- all departments together make up the whole month's sales.
- That means it's parts of a whole, which is exactly what a pie chart is designed to show.
- A bar chart could also compare the departments, but a pie chart makes the 'parts of the whole' relationship clearer.
Try it
Ask what the data is really doing -- comparing categories, changing over time, splitting a whole, or linking two variables -- before choosing.
Question 1
A gardener records plant height every week for 10 weeks. Which graph is best?
Question 2
A survey asks 100 people their favourite pizza topping (4 options). Which graph best compares the options?
Question 3
A scientist wants to check whether hours of exercise are linked to resting heart rate. Which graph is best?
Question 4
A charity wants to show how its total annual budget splits between 5 project areas. Which graph is best?
Question 5
Why is a pie chart a poor choice for showing a company's monthly profit over 12 months?
Common mistakes
Watch for these when working through the lesson.
- Using a pie chart for data that changes over time.
- Using a line graph for categories that have no natural order (like favourite colours).
- Choosing a scatter graph when there's only one variable being measured, not two.
Related topics
These ideas fit closely with this lesson.
- Draw and interpret pie charts.
- Scatter graphs, line of best fit and correlation.
- Construct bar charts, pictograms and frequency tables.