Comet draws a giant circle on the whiteboard and splits it into four slices.
"A pie chart!" she says. "One slice for each Q3 choice. It looks great."
Wren reads the council's note again. It says they want to know which addition members asked for most.
"What do you notice about their question?" he asks. "Are they asking about parts of a whole, or about which group is biggest?"
Comet taps the marker against her chin. "Maybe both?"
Nova projects the Q3 table beside the circle. "Would you like a hint?" she asks.
"Each kind of graph is good at a different job. Match the job to the council's question."
Comet grins. "So the right graph depends on the question. Let's find out which one fits."
Bar graphs compare things between different groups. They can also track changes over time, and they work best when those changes are large.
Pie charts are best for comparing parts of a whole. They do not show changes over time.
| Graph | Good at | Not for |
|---|---|---|
| Bar graph | Comparing groups; larger changes over time | Tiny changes over time |
| Pie chart | Parts of a whole | Changes over time |
On a bar graph, the y-axis usually holds the numbers for the amount being measured.
It usually starts counting at 0.
It can be split into as many parts as you want, but the parts are equal.
The tallest Q3 bar is 13, so a y-axis from 0 to 14 gives every bar room.
| Q3 answer (valid only) | Members |
|---|---|
| Longer evening hours | 13 |
| Quiet study room | 11 |
| Repair bench | 9 |
| Bike rack | 5 |
| Total valid | 38 |
Made-up data from the Commons Count story.
| Statement | True or false? |
|---|---|
| Pie charts compare parts of a whole. | ? |
| Pie charts show how things change over time. | ? |
| Bar graphs can compare things between different groups. | ? |
| The y-axis on a bar graph usually starts at 0. | ? |
| The steps on a y-axis can be any size, as long as the numbers go up. | ? |
Clear thinking, data analyst. Tomorrow in Count Lab you will draw the Q3 bar graph by hand.