Correlation and regression

The coefficient r, explained variance, the regression line and the difference between correlation and causation.

The outline, topic by topic

Each topic is weighted the way the exam weighs it.

Correlation: what is it?
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A statistical link between two variables that vary together.
It does not say which causes the other.
The more members a club has, the more injuries it has. What can we conclude?
- Nothing about risk: the injury rate per member must be compared
- Big clubs expose their members to more injuries
- Injuries push people to join a club
- The number of members per club should be capped
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Nothing about risk: the injury rate per member must be compared
More members means more people exposed: the number of injuries rises mechanically, and only a rate compares the risk.
Pearson's coefficient (r): what is it?
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A measure of the strength and direction of a linear link, from −1 to +1.
0 means no linear link, not necessarily no link at all.