Reading graphs and statistics
Reading graphs and statistics: a chapter of the Thinking Clearly Book, with the mind traps and tricks that are worth knowing by name.
11 cards · Science
Each Zap teaches up to 5 new cards, so you learn the chapter a few at a time.
Checked by the Brain Zap team · reviewed 27 Oct 2026
Sources: Statistical literacy (Royal Statistical Society), News literacy (News Literacy Project)
Preview
A bar chart whose axis doesn't start at zero
Show answerHide answer: A bar chart whose axis doesn't start at zero
A truncated axis
Learn more: Cutting off the bottom of the axis exaggerates differences; always check where the scale starts.
Axis where each step multiplies by 10
Show answerHide answer: Axis where each step multiplies by 10
Log scale
Learn more: Useful for epidemics and money, but it can hide how fast things are really rising.
Choosing only the dates that tell your story
Show answerHide answer: Choosing only the dates that tell your story
Cherry-picking
Learn more: Start or end a chart at the right moment and almost any trend appears; ask what the full record shows.
"Doubles the risk", with no starting number
Show answerHide answer: "Doubles the risk", with no starting number
Relative risk
Learn more: Always ask for the absolute risk: going from 1 in a million to 2 in a million is "double".
The ±3% that comes with a poll
Show answerHide answer: The ±3% that comes with a poll
Margin of error
Learn more: A 2-point lead inside a ±3% margin is too close to call.
About this topic
A chart can mislead without a single false number. An axis that doesn't start at zero makes small gaps look huge, a log scale tames fast growth, and a well-chosen start date can make almost any trend appear. This chapter teaches the questions to ask of any graph or statistic: where the scale starts, what the absolute numbers are, how big the margin of error is, who was asked, and whether two things moving together really have anything to do with each other.
This is a chapter of the Thinking Clearly Book. Each card asks one question, with a hint before you answer and a short reason after. Once you know most of this chapter, the next one starts arriving in your Daily Zap.
All 11 cards
A bar chart whose axis doesn't start at zero
A truncated axis
Learn more: Cutting off the bottom of the axis exaggerates differences; always check where the scale starts.
Axis where each step multiplies by 10
Log scale
Learn more: Useful for epidemics and money, but it can hide how fast things are really rising.
Choosing only the dates that tell your story
Cherry-picking
Learn more: Start or end a chart at the right moment and almost any trend appears; ask what the full record shows.
"Doubles the risk", with no starting number
Relative risk
Learn more: Always ask for the absolute risk: going from 1 in a million to 2 in a million is "double".
The ±3% that comes with a poll
Margin of error
Learn more: A 2-point lead inside a ±3% margin is too close to call.
A poll that only asks people online at noon
Selection bias
Learn more: If the sample isn't like the population, even a huge poll can be wrong.
From 10% to 12% is a rise of 2…
Percentage points
Learn more: From 10% to 12% is 2 percentage points but a 20% rise: both are true, and they sound very different.
A pie chart's slices should add up to
100%
Learn more: If the slices add up to more than the whole, the chart is mixing up categories.
One value far from all the others
An outlier
Learn more: One billionaire in a room lifts the average income hugely; the median barely moves.
Cheese eaten tracks deaths by bedsheet tangling
Spurious correlation
Learn more: With enough data sets, some move together by pure chance; that is not cause and effect.
Comparing countries fairly by dividing by population
Per capita
Learn more: China emits the most CO₂ in total; per person, the US emits more.
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