Name: Ice Cream Sales and Shark Attacks [Correlation vs Causation]
Uploaded: 2026-03-28T17:36:34.000Z
Duration: 4 min 51 s
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There is a famous graph that shows ice cream sales and shark attacks,

Modal verbs - B1

In statistics, we must differ between correlation and causation.

Correlation means two things move together at the same time.

Causation means one thing causes a change in the other.

Correlations can be positive, negative, or zero.

Think of ice cream sales and shark attacks, ice cream and raincoat sales, and

ice cream and the number of pirates worldwide.

They can be weak, strong, or even perfect, like hours playing video games and slices of pizza eaten, time spent studying versus test scores, the number of left and right socks produced.

Causations exist if one thing affects others, often multiple things.

The effect can be strong or weak, and between effects we often see correlations.

Our brains love simple stories, such as X causes Y.

This is why when we see a strong correlation, say kids' shoe size and reading ability, we may think of causation.

But three solutions help us avoid these errors.

As kids grow, they need larger shoes and get better at reading.

If a third factor drives correlating results, we call it confounding.

We may think that ice cream makes people happy,

but maybe happy people just have more reasons to buy ice cream.

Spurious correlation exists when patterns appear by chance.

For example, as the number of pirates decreased, we recorded increasingly hotter days,

There are three questions to test a causal claim.

Suppose someone claims that students who sleep more get better grades.

Does longer sleep come before better grades?

Two organised students maybe do both, sleep more and study more.

Sleep may boost attention and memory, but can it explain better grades?

To look for a real causal link, serious social scientists typically turn to three methods.

In randomised, controlled trials, people are randomly put into two different situations, say school classes with 15 students and classes with 25.

Scientists then look at what happens and may find that one group learns faster than the other.

Ideally, that experiment then gets replicated.

RCTs are considered the gold standard of research.

Natural experiments are real-world events that create as-if random groups.

In 1980, 125,000 Cuban refugees arrived in Miami almost overnight.

With all these new workers, local employees feared for their jobs.

But economists later compared the situation in Miami to similar cities and found wages were hardly affected.

Longitudinal studies tracked the same people over many years to check time order.

The Grant study, for example, tracked 268 Harvard-educated men since 1938.

It found that alcoholism was the main cause of a divorce and that men who earned more typically had warm childhood relationships with their mothers.

To help us find a causal link, it's useful to compare apples with apples, such as grouping people by age, income, or lifestyle when we study them.

Imagine you see this headline: "Kids with more books at home do better in school." First, ask yourself the three questions to test the causal claim and then design a test to find out.

Share your findings in the comments below.

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