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# Correlation and Causation

## Correlation means that two trends go together; causation means that one of those trends causes the other.

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Practice Correlation and Causation
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Estimated7 minsto complete
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Ice Cream Causes Polio

### Ice Cream Causes Polio

Credit: Centers for Disease Control and Prevention
Source: http://en.wikipedia.org/wiki/File:Polio_physical_therapy.jpg

Polio once crippled thousands of people, mostly children. Polio epidemics were during summer and fall. People eat more ice cream during summer and fall. So for a while, children were warned not to eat ice cream or they would get polio.

#### Why It Matters

• Correlation and causation are not the same thing.
• Correlation is worth nothing. It just means two trends are going in the same direction.
• If two trends are correlated, one may be causing the other to happen. This is causation.
• People waste a lot of time and may do damage trying to stop things that are only linked by correlation.
• Sometimes the relationship is backwards. People think A causes B, but really B causes A.
• Sometimes, as in the polio and ice cream example, they are related by a third factor. Polio and ice cream consumption both increase in the summertime. Summer is when the polio virus thrived. Check out the short clip about this example below:

#### Can You Apply It?

1. Correlation: Marriage (A) and longevity is (B). Describe the correlation (do not assign a cause). Which did people think was the cause of the other? What is more likely to the cause of the other? Or is there a third factor; if so, what is it?
2. Correlation: Sleeping with the lights on is (A) and shortsightedness (nearsightedness) is (B). Describe the correlation (do not assign a cause). Which did people think was the cause of the other? What is more likely to the cause of the other? Or is there a third factor; if so, what is it?
3. Correlation: Kids who do well in school is (A) and high self esteem is (B). Describe the correlation (do not assign a cause). Which did people think was the cause of the other? What is more likely to the cause of the other? Or is there a third factor; if so, what is it?
4. Why does she say that the conclusion that high self-esteem causes kids to do well in school is the worst example of incorrectly identifying cause?

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