Curriculum
Statistics — Third Secondary
Unit 1: Correlation and Regression
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Unit 2: Advanced Statistical Measures
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Unit 3: Probability
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Unit 4: Random Variables
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Unit 5: The Normal Distribution
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Text lesson
Correlation
Correlation
Strength of correlation and the coefficient r
Strength of correlation and the coefficient r
- The strength of the relationship is measured by the correlation coefficient r.
- Its value always lies between −1 and +1.
- The sign shows the direction, and the size (absolute value) shows the strength.
| Value of r | Meaning |
|---|---|
| +1 | Perfect positive correlation: all points lie on a straight line rising to the right |
| −1 | Perfect negative correlation: all points lie on a straight line falling to the right |
| 0 | No linear correlation between the two variables |
| Close to +1 or −1, for example 0.9 or −0.95 | Strong correlation |
| Close to 0, for example 0.2 or −0.1 | Weak correlation |
- The closer the absolute value of r is to 1, the closer the points are to a straight line and the stronger the correlation.
- So r = −0.9 means a strong negative correlation, and r = 0.2 means a weak positive correlation.
- Note that r = 0 means there is no linear correlation only.
- It does not necessarily mean there is no relationship at all, because a non-linear relationship may exist.
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