In a presentation
A slide shows two bars. One is roughly twice the height of the other. You look at the axis: it starts at 94 and ends at 98.
What is the real difference?
Step 1: What Would You Do?
There is often more than one good answer. Pick one and see what happens.
Online
A post shows that towns with more libraries have higher exam results, and concludes that building libraries raises results.
What is the gap in that reasoning?
Step 2: What That Was
The name for what you just worked out.
The bottom of a bar chart does not have to be zero. When it is not, a tiny difference can be drawn as a huge one. Nothing is false; the picture is just wrong.
Which years?
A line that goes up over five years may go down over twenty. Whoever chose the years chose the story.
What is not on it
A chart of one thing rising says nothing about whether everything else rose too. Ask what would have to be on it to change your mind.
Two lines together
Two things rising at the same time does not mean one caused the other. Ice cream sales and sunburn rise together. Neither causes the other.
Step 3: Try It
These ones do have right answers.
Fair or Aimed?
Sort each chart choice.
Which of these make a chart harder to read honestly?
Tap something to move it.
- Empty
- Empty
Step 4: Quick Check
Two questions, then you are done.
Question 1 of 1
A chart shows your town’s recycling rising sharply since 2021. What is worth checking?
Step 5: Your Life Mission
Something to do away from the screen. Nobody is checking.
Find one aimed chart
- Find a chart this week — news, advert, anywhere.
- Check where the axis starts and which years it covers.
- Write one sentence on what it wants you to conclude.
Why: Once you have found one, you cannot stop seeing them.
Step 6: What You Learned
- Check where the axis starts and whether it is labeled.
- Ask who chose the years, and why those years.
- Two things rising together does not mean one caused the other.
For the grown-up
This is not the same as the chart-reading in the math courses. There the task is to read the chart correctly; here it is to notice that a correctly-read chart can still have been built to lead you. Both are needed and they are separate skills.
Charts in the wild are the best material — a news graphic, an advert, a chart in a shop window. Asking "where does the axis start?" together takes ten seconds and becomes automatic quickly.
The correlation point is worth repeating whenever it comes up naturally, because it is one of the few pieces of statistical thinking that people either have or spend their lives without.