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Spot a misleading chart

Per-person rates, dual axes, running totals and stretched icons: how charts mislead, and what to check. Pairs with Stats that fool you.

16 cards·by braineos-team
datacritical-thinkingstatistics
Study this deckPlay Tower Defense
Per capita
Per person. Big countries have big totals, so divide by population to compare fairly.
Dual axes
Two lines on one chart, each with its own scale. Stretch either scale and they seem to move together.
Running total
A cumulative count. It never goes down, so it can hide a slowdown.
Chosen start date
Starting a chart at an unusually high or low point, so the trend looks bigger or even reversed.
Stretched icon
Doubling a picture's height and width to show "twice as much" makes it look four times bigger.
3D chart
Tilting a pie or bar chart makes the parts nearest you look bigger than they are.
Uneven intervals
Spacing dates unevenly along an axis, like 2000, 2010, 2020, 2021, which bends the trend's shape.
Inflation-adjusted
Old money figures restated in today's money. Without it, the past always looks cheap and small.
Country A has five times as many bike thefts as Country B. What do you need before calling A worse?
  1. A bar chart instead of a line
  2. ✓ Each country's population
  3. Last year's total for A
  4. Brighter colours
A bar chart's y-axis starts at 95, and a bar for 98 looks three times as tall as one for 96. What's wrong?
  1. ✓ The axis is cut off, so a small gap looks big
  2. The bars should be 3D
  3. There are too few bars
  4. The bars are the wrong colour
A chart of total sign-ups climbs every month. Can you tell whether growth is slowing?
  1. Yes, it's speeding up
  2. ✓ Not from a running total; look at sign-ups each month
  3. Yes, if the line is steep
  4. Only if it's a pie chart
Two lines on separate left and right scales track each other closely. What's the catch?
  1. ✓ Either scale can be stretched to make the lines match
  2. The lines must be the same colour
  3. The chart needs a title
  4. Lines can't cross
A poster shows a coin icon twice as tall and twice as wide to mean "double the savings". How big does it look?
  1. Exactly twice as big
  2. ✓ About four times as big
  3. The same size
  4. Half as big
A pie chart's slices add up to 130%. What does that tell you?
  1. The data is extra accurate
  2. One slice is in 3D
  3. ✓ People could pick more than one answer, so a pie is the wrong chart
  4. It's per capita
"This 1970s film earned less than this year's hit." What would make the comparison fair?
  1. The films' running times
  2. ✓ The figures adjusted for inflation
  3. The number of sequels
  4. The poster designs
A chart of a city's crime begins in the year crime was lowest in a decade. What should you ask?
  1. ✓ What the trend looks like over a longer range
  2. Whether the line should be thicker
  3. Whether it has a legend
  4. How many colours it uses