Skip to content

Infographics

Statistics and data · level 4, lesson 4 of 6

A question to start

A poster in a school hallway shows a giant number, 38%, next to a drawing of an apple core. Underneath, in small letters: "of students threw away food at lunch."

Most people walking past will remember that poster. But stop and think like a statistician. 38% of which students? How many were asked? Threw away food every day, or once? Who made the poster, and why?

An infographic is a picture that tells a story with data. Good ones are among the clearest ways ever invented to share numbers. Careless or sneaky ones can make you believe something the data never said. In this lesson you learn to read them, to judge them, and to plan one yourself.

The idea

What an infographic is

An infographic ("information graphic") combines several pieces on one page:

  • a headline that states the main message;
  • big numbers ("38%", "1 in 4") that catch the eye;
  • charts: bar graphs, circle graphs, line graphs, from levels 2 to 4;
  • icons or pictographs: little pictures, each standing for an amount;
  • short text that explains what each number means;
  • a source: who collected the data, how, when and from how many.

The goal is to tell one story quickly, so that someone glancing at it for ten seconds understands the main point, and someone reading carefully finds the details to check it.

A worked example of an infographic

Here is an infographic made by a student council after a survey.

Lunch waste at our school 38% threw away some food every day (76 of 200 students) Items thrown away in one week VegetablesFruit SandwichesOther 60453015 1 in 4 students brings a reusable container (50 of 200) Source: student council survey of 200 students, one school week. Bars count food items.

Read it like a statistician:

  • The headline says what it is about: lunch waste at one school.
  • The big number, 38%, is explained: 76 of 200 students. Check: \(\frac{76}{200} = 0.38 = 38\%\) ✓. The icons show 2 of 5 shaded, which is 40%: close to 38%, a fair rounding ("about 2 in 5").
  • The bar chart starts at zero (every bar starts at the same line) and the bars are in proportion: 60 is twice 30, and the vegetables bar (96 units long) is twice the sandwiches bar (48). It tells the second part of the story: most waste is vegetables.
  • "1 in 4" is checked against the count: \(\frac{50}{200} = \frac{1}{4}\) ✓.
  • The source tells you who asked (the student council), how many (200), and when (one week).

The story it tells: a large share of students waste food, vegetables most of all, and few bring reusable containers. Every number is explained and checkable.

Judging an infographic: is it clear?

Ask these questions:

  1. Is there one main message, stated in the headline? A page crammed with twenty unrelated numbers is a scrapbook, not an infographic.
  2. Does every number say what it is a number of? "38%" alone is useless. 38% of whom, doing what?
  3. Are the charts the right kind? Parts of a whole in a circle graph; comparisons in bars; change over time in a line (lessons 2 and 3, and level 3).
  4. Can you read it? Labels on the charts, units, not too much text, colours that are easy to tell apart.

Judging an infographic: is it honest?

Clear is not the same as honest. Ask:

  1. Is there a source? Who collected the data, how, when, from how many? No source means you cannot check anything.
  2. Do the numbers add up? Percents of one whole should total 100%. "1 in 4" should match the count. Check the arithmetic yourself: it takes seconds.
  3. Are the pictures to scale? A bar twice as long should stand for twice the amount; an icon row with 2 of 5 shaded should mean about 40%. (Lesson 6 shows tricks with pictures that grow in two directions.)
  4. Is the comparison fair? Comparing totals between a big school and a small school is unfair; compare percents.
  5. Who made it, and what do they want? A company selling lunchboxes might choose to show only the scariest numbers. That does not make the numbers false, but it means you should ask what was left out.
  6. Does the headline say more than the data? "Students don't care about the planet!" is not shown by any number on the lunch poster. A headline must match what was actually measured.

Planning your own

  1. Start with your question and your data (lesson 1 of level 3).
  2. Decide your one message in a sentence.
  3. Pick two to four facts that support it. For each, choose a big number, a chart or an icon row.
  4. Check every number against the data, and every picture against its number.
  5. Add a source line. Show a friend for ten seconds and ask what the message was. If they cannot say, simplify.

Worked examples

1. Checking the numbers. An infographic says: "Survey of 80 students. Favourite subject: Math 30%, Art 25%, Science 20%, Gym 15%, Music 15%."

  1. Add the percents: \(30 + 25 + 20 + 15 + 15 = 105\%\). Too much.
  2. Either a percent is wrong, or students chose more than one subject. Check with counts: 30% of 80 is 24, 25% is 20, 20% is 16, 15% is 12 and 12. That makes \(24 + 20 + 16 + 12 + 12 = 84\) students, more than 80.
  3. The infographic must explain this ("students could choose two") or be fixed; and if students could choose more than one, it must not use a circle graph.

2. "1 in 3" to a percent. An infographic says "1 in 3 Canadians ..." That is \(\frac{1}{3}\), about 33%. An icon row of 3 people with 1 shaded shows it exactly. If the data said 31%, "about 1 in 3" is fair; if the data said 25%, "1 in 3" is not (\(\frac{1}{4}\) would be right).

3. Spotting a misleading headline. An infographic shows that sales of bicycle helmets in a town went up from 400 to 500 in a year, and headlines it "Everyone is wearing helmets now!"

  1. The rise is \(500 - 400 = 100\), which is \(\frac{100}{400} = 25\%\) more than before.
  2. But helmets sold is not the same as people wearing helmets, and 500 helmets in a whole town is not "everyone". The headline claims far more than the data show. An honest headline: "Helmet sales up 25% this year".

4. Planning from a table. A class measured how many minutes each student read daily: under 15 min, 6 students; 15-29 min, 10; 30-44 min, 8; 45 min or more, 6 (30 students). A plan: message "Most of us read at least 15 minutes a day". Big number: \(\frac{10 + 8 + 6}{30} = \frac{24}{30} = 80\%\). A histogram-style bar chart of the four groups (these are intervals of a number, so the bars should touch). Source: "class survey of 30 students, one week".

Try it

  1. An infographic shows "45%" in big letters with no other words. Give two questions you would ask.
  2. A row of 10 icons has 3 shaded and is labelled "28% walk to school". Is that fair? What about 7 shaded?
  3. "1 in 5 students plays a musical instrument". What percent is that? How many would that be in a school of 350?
  4. An infographic's circle graph has slices of 50%, 30% and 30%. What is wrong?
  5. Two schools: "School A recycled 2000 cans, School B only 900!" School A has 1000 students, School B 300. Who recycled more per student?
  6. Write an honest headline for this data: in a survey of 50 students, 32 said they would like a longer lunch break.
  7. A sports drink company's infographic says "9 out of 10 athletes prefer our drink". Give two honesty questions you would ask.
Answers
  1. For example: 45% of whom? 45% doing what? How many were asked, and who asked them?
  2. 3 of 10 is 30%, close to 28%: fair. 7 shaded would be 70%: not fair.
  3. \(\frac{1}{5} = 20\%\). \(\frac{1}{5}\) of 350 is \(350 \div 5 = 70\) students.
  4. \(50 + 30 + 30 = 110\%\). The parts of one whole must add to 100%.
  5. A: \(2000 \div 1000 = 2\) cans per student. B: \(900 \div 300 = 3\) cans per student. School B recycled more per student, though its total was smaller.
  6. For example: "Most students asked want a longer lunch: 32 of 50 (64%)". Check: \(\frac{32}{50} = 0.64 = 64\%\).
  7. For example: How many athletes were asked, and how were they chosen? What were they comparing the drink with? Who paid for the survey? Were athletes who preferred other drinks left out?

Common mistake

Believing the big number without reading the small print. The biggest number on the page is the one the designer wants you to remember; it is not always the most important. Read what it is a percent of, and look for the source.

Mixing up "more" and "most". 38% is a lot, but it is not "most students". Most means more than half, more than 50%.

Where it leads