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Correlation

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Correlation

Quantitative assessment of the strength of the relationship between x & y.

It is the measure of the extent to which x & y are linearly related.

*It is strong if the points lie close to a straight lint and is weak if they are widely scattered about a line.

- It’s a number between -1 and 1.
- The closer it is to the ends, the stronger the positive or negative relationship.
- It gives the strength and direction.

Strong Negative

No Correlation

Strong Positive

-1

1

0

- www.whfreeman.com/tps4e

Think about z-scores of the x & y

Think about z-scores of the x & y

Think about z-scores of the x & y

r

If you are asked to interpret a correlation start by looking at a scatterplot of the data. Then be sure to address direction, form, strength, and outliers and put your answer in context.

- It does not depend on the unit of measurement.
- It doesn’t depend upon which of the 2 variables is “x”
- It’s between -1 and 1
- It equals -1 or 1 if all points lie on a straight line
- It is strongly affected by a few outliers

Scatterplots show relationships – not cause and effect.

- Create scatterplot
- Find the correlation
- Describe the association

- Page 160 (14-18, 21, 26)