Start at the edges, not the shape
A chart is an argument wearing a picture. Before you react to the shape of the line, read the edges: the title, the two axes, the units, and the source. Those four things tell you what question the chart claims to answer.
Most people read charts the other way. They see the line spike, feel something, and share it. By the end of this lesson you will be slower than that, on purpose.
The three classic tricks
Trick one: the truncated axis. If the y-axis starts at 95 instead of 0, a 2 percent change looks like a cliff. Trick two: the cherry-picked window. Start a temperature chart in an unusually hot year and you can make warming look like cooling. Trick three: missing units. A chart of 'flood incidents' means nothing until you know who counted and how.
None of these tricks require lying about the data. That is what makes them dangerous. The numbers are real. The frame does the lying.
Practice on the real thing
Open Our World in Data and pull up Nigeria's average temperature. Check the axes. Check the window. Ask what would change if the chart started 20 years earlier or later.
This is the habit: source, axes, window, then opinion. In that order. Every lesson in this course repeats it until it is a reflex.
Hold on to these
- Read title, axes, units and source before reacting to the shape.
- Truncated axes, cherry-picked windows and missing units mislead without faking data.
- The order is source, axes, window, then opinion.
Check yourself
No grades here. If you can answer these out loud, you own the lesson.
- 1.Why can a truncated y-axis make a small change look dramatic?
- 2.How would you check whether a temperature chart's time window was chosen fairly?
- 3.Find any chart in a news story this week. What are its axes, units and source?