# Correlation - PowerPoint PPT Presentation

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Correlation. Correlation Coefficient (r). 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.

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Correlation

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## Correlation

### Correlation Coefficient (r)

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.

### Correlation (r)

• 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

### Let’s explore….

• www.whfreeman.com/tps4e

### Pearson’s Correlation Coefficient

Think about z-scores of the x & y

### Pearson’s Correlation Coefficient

Think about z-scores of the x & y

### Pearson’s Correlation Coefficient

Think about z-scores of the x & y

r

### AP Exam Tip

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.

### Properties of “r”

• 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.

### Try One!

• Create scatterplot

• Find the correlation

• Describe the association

### Homework

• Page 160 (14-18, 21, 26)