Lesson 1 — Correlation Is Not Causation

Summary

Learners meet the most important idea in reading evidence: two things happening together (correlation) does not prove one causes the other (causation). They learn to look for a hidden third variable, and sort everyday pairs into “correlation” and “causation” — building the lifelong habit of asking “what else could be going on?”

Objectives

• Distinguish correlation from causation and explain why a pattern alone does not prove a cause. (D06.S1.07.01)

Connection

Every summer, in cities all over the world, two numbers rise together: ice cream sales and the number of people who go swimming in rivers and lakes — and, sadly, sometimes drownings. Does ice cream cause drowning? Of course not. Both rise because of a third thing: hot weather sends people to buy ice cream and to the water. The two numbers are correlated — they move together — but neither causes the other. Telling the difference is a skill you will use every day, from reading a headline to deciding whether a medicine actually works.

Materials

• Correlation-or-causation card set
• Third-variable page
• Pencils and highlighters

Preparation

• Copy the correlation-or-causation card set for pairs and the third-variable page for each learner.
• Have the worked example ready: ice cream sales and drownings both rise in summer; the third variable is hot weather.
• Recall from Grade 6: distinguishing evidence, inference, and opinion (D06.S1.05.02), and spotting bias in an investigation (D06.S1.06.02).

Facilitator note

This lesson is written to the learner (“you”). The idea to land is precise: correlation (two things move together) is not causation (one makes the other happen), because a third variable may cause both. Because this is a foundational reasoning skill, use explicit instruction and a worked example first (Kirschner, Sweller & Clark, 2006): model the ice-cream-and-drowning example aloud, then guide one more before independent sorting. Watch for the common slip of assuming “they happen together, so one must cause the other.” The distinction between correlation and causation is a foundational principle of statistics and scientific reasoning, taught across the world’s science curricula; the “spurious correlation” idea (a shared third cause) is its heart. The ethical and egalitarian lenses (docs/philosophy.md §4): confusing correlation with causation is how people get blamed unfairly — a neighborhood blamed for a trend it did not cause, a group blamed for an outcome driven by poverty or history. Questioning the pattern is a tool of fairness. The global lens: the ice-cream example works because hot weather is universal, but adapt it — in some places it is mango season, monsoon, or a festival, not ice cream, that marks the “third variable.”

Procedure

1. Gather (5 min). Think of two things you have noticed happening together. Did one cause the other? Today you learn to tell the difference — and when to say “not enough evidence.”
2. Meet the two words (10 min). Correlation = two things change together (when one goes up, the other goes up). Causation = one thing makes the other happen. Worked example: ice cream sales and drownings rise together (correlation). Does ice cream cause drowning? No — a third variable, hot summer weather, causes both.
3. The rule (5 min). A pattern alone — even a strong one — does not prove a cause. Before you say “X causes Y,” ask: Could a third thing cause both? If yes, the pattern is spurious — it looks like a cause but is not.
4. Sort with a partner (20 min). Take your card set. For each pair, draw three boxes on your page: effect A, effect B, and the possible third cause. Decide together: correlation or causation? (Examples: stork nests and human births rise together in some old records — is it the storks? Or does a third thing — countryside with more farms — explain both?)
5. Defend one (5 min). Pick one pair and say in one sentence: “These are correlated because ___, but ___ might cause both, so I need more evidence to say one causes the other.”
6. Close (5 min). The habit: when two things move together, ask “what else could be going on?” You will use this every day of your life.

Differentiation

• Support: Use only the ice-cream example and two simple pairs; describe each aloud so learners with low vision can follow by listening, and draw the three boxes together.
• Extension: For one example, also consider reverse causation (could B cause A?) and say which explanation the pattern alone cannot decide.

Assessment

• Formative (observation/self): Can the learner sort a new pair as correlation or causation and name a possible third variable?
• Self-check: The learner asks, “Did I name a third thing that could cause both? Does my answer say why the pattern alone is not enough?”

Home connection

Find a headline, ad, or claim you hear this week that says one thing causes another. Ask at home: could a third thing cause both? Bring your example to share next time.

Resources

• The distinction between correlation and causation is foundational to statistics and scientific reasoning; a classic, accessible collection of real spurious correlations is Tyler Vigen, Spurious Correlations (spuriouscorrelations.com). The ice-cream/drowning example is a standard illustration of a common cause (confounding). The value claim that questioning a pattern protects people from unfair blame is a value commitment, not a statistical fact (docs/philosophy.md §5).
• On modeling a new skill before independent practice: Kirschner, Sweller & Clark (2006), https://doi.org/10.1207/s15326985ep4102_1