Lesson 1: Truncated Axes and Stretched Scales

About 30 minutes — Activity-based lesson

What You Will Learn

This lesson covers:

What a truncated y-axis is and why it misleads
How stretched or compressed scales distort perception
The 'zoom in' trick: making small changes look dramatic
Activity: compare honest vs. misleading versions of the same data

What a truncated y-axis is and why it misleads

This section covers the key ideas about what a truncated y-axis is and why it misleads. Discuss with your group or family and explore the concepts together.

How stretched or compressed scales distort perception

This section covers the key ideas about how stretched or compressed scales distort perception. Discuss with your group or family and explore the concepts together.

The 'zoom in' trick: making small changes look dramatic

This section covers the key ideas about the 'zoom in' trick: making small changes look dramatic. Discuss with your group or family and explore the concepts together.

Activity: compare honest vs. misleading versions of the same data

This section covers the key ideas about activity: compare honest vs. misleading versions of the same data. Discuss with your group or family and explore the concepts together.

Check Your Understanding

1. What is a truncated y-axis?

Answer: When a graph's number scale starts above zero, making small differences look enormous. A bar from 98 to 100 looks tiny on a 0-100 scale but massive on a 98-100 scale.

2. How does stretching a scale mislead?

Answer: By making changes appear larger or smaller than they really are. Stretching the y-axis exaggerates differences; compressing it minimizes them.

3. How can you spot a truncated axis?

Answer: Always check where the y-axis starts. If it does not start at zero, ask yourself: how would this graph look with a full scale?

4. Is truncating the axis always wrong?

Answer: Not always — sometimes zooming in is useful for seeing small but real patterns. But it should always be labeled clearly so readers know the scale is zoomed.

Key Takeaways

What a truncated y-axis is and why it misleads
How stretched or compressed scales distort perception
The 'zoom in' trick: making small changes look dramatic
Activity: compare honest vs. misleading versions of the same data

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Continue to Lesson 2: Cherry-Picking and Missing Context

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