The bar that grew by magic
Two bars show lunches sold on sunny and rainy days. Sunny is a little higher. On one chart the sunny bar looks ten times taller.
Both charts use the same data. One of them misleads. You will learn to spot why.
Key words
| Word | What it means | Example |
|---|---|---|
| Axis | The line along the edge of a chart that carries the scale and labels. | Lunches sold up the side |
| Scale | The steps of numbers along an axis. | 0, 100, 200, 300 |
| Cut axis | An axis that does not start at zero, which makes small gaps look big. | Bars starting at 220 |
| Misleading | Giving a wrong idea even if every number is true. | A cut axis |
| Label | Words on a chart that say what each part is. | Meals sold per day |
| Source | Where the data came from. | Canteen till log, autumn term |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can present data in a visual that is honest, and spot a cut axis and a crowded 3D pie.
Starter: what you already know
Have a go
Starter: what you already know
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Rules for an honest visual
Start a bar chart axis at zero, because the length of a bar stands for its size. Give a clear title and label both axes with units. Name the source.
Use the same scale when you compare two charts. Use colour to help, not to decorate.
Five described charts and what is wrong
| Described chart | Problem | Fix |
|---|---|---|
| Bars start at 220, not 0 | Small gap looks huge | Start the axis at 0 |
| A 3D pie with eleven slices, tilted | The front slices look bigger and small ones cannot be read | Use a flat bar chart |
| A line graph with no unit on the side | The reader cannot tell what is counted | Label the axis with units |
| Red and green used as the only key | Some readers cannot tell them apart | Add labels or patterns |
| No source or date | The reader cannot judge the data | Add the source and date |
The cells students fill in are left blank in this preview.
Check: spot the problem
Have a go
Check: spot the problem
4 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.