Comet unrolls a huge, bright poster across the workbench. Orange bars shoot up the page.
"Look at longer evening hours," she says proudly. "It towers over the bike rack. Nine times taller!"
Wren tilts his head. "The table says 13 and 5. That is not nine times."
"What do you notice about where your y-axis starts?" he asks.
Comet looks down. The first number on her axis is 4, not 0. "I wanted the bars to fit the poster," she says.
Nova hovers above the poster and projects a faint ruler beside each bar. "Would you like a hint?" she asks.
"Count the steps in each bar. Then compare those steps with the numbers in the table."
Comet laughs. "My first draft is a puzzle. Let's solve it."
How can a true number tell a false story?
This week you will find what makes a chart mislead, redraw it honestly and check claims against the whole data.
On a bar graph, the y-axis usually starts counting at 0 and is split into equal parts.
Comet's y-axis starts at 4. So each bar shows only the part of its number above 4.
The longer evening hours bar shows 13 minus 4, which is 9 steps. The bike rack bar shows 5 minus 4, which is 1 step.
| Q3 answer | Members | Steps on Comet's poster (from 4) | Steps on an honest graph (from 0) |
|---|---|---|---|
| Longer evening hours | 13 | 9 | 13 |
| Quiet study room | 11 | 7 | 11 |
| Repair bench | 9 | 5 | 9 |
| Bike rack | 5 | 1 | 5 |
Made-up data from the Commons Count story.
| Statement | True or false? |
|---|---|
| Comet's numbers were wrong. | ? |
| Comet's bars did not match the size of her numbers. | ? |
| On a bar graph, the y-axis usually starts at 0. | ? |
| A chart can use true numbers and still give a false picture. | ? |
Great detective work, data analyst. Tomorrow you will find more ways a chart can go wrong.