M3.7.5 For the adult
Line graphs and honest charts
Two graphs show the same numbers. Why does one line climb so much more steeply?
What this chapter teaches
A line graph shows change over time. A bar chart must start at zero. A graph whose scale is cut makes small changes look big, so it needs a zigzag. Check the first number on the axis before you trust a picture.
Three questions to ask
There is no one right wording. Listen for the idea.
- What do you look at first on a graph before you trust it?
- The same numbers drawn from 0 and from 40: how do the two lines differ?
- Why is a zigzag on an axis a kind thing for a graph to show?
After the chapter, the learner can
- Draw a line graph for data that changes over time
- Spot a chart that misleads by not starting at zero
What they copy into their notebook
A line graph shows change over time. Join the points with straight lines. Read the scale before you read the picture. A bar chart starts at 0. A cut line graph needs a zigzag.