# Correlation - PowerPoint PPT Presentation

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Correlation. Topics. Measure of Relationship Strength Direction Scatterplot Conceptual Formula Computational Formula Assumptions Problems Effecting the Interpretation of the Correlation Coefficient. Measure of Relationship.

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Correlation

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## Correlation

### Topics

• Measure of Relationship

• Strength

• Direction

• Scatterplot

• Conceptual Formula

• Computational Formula

• Assumptions

• Problems Effecting the Interpretation of the Correlation Coefficient

### Measure of Relationship

• In a correlational study, two measures -- representing the variables of interest -- are given to onegroup of subjects.

• The subject’s scores on both measures are summarized, and the relationship between the scores on the two measures is examined.

### Measure of Relationship

• When the correlation coefficient is used to describe a linear relationship, the coefficient can take on values from -1.00 to +1.00.

• The sign of the correlation indicates the direction of the relationship between two variables.

### Measure of Relationship

• A positive relationship means that low scores on X go with low scores on Y whereas high scores on X go with high scores on Y.

• A negative relationship means that as scores on X increase, scores on Y decrease.

• The absolute magnitude or size of the correlation coefficient -- that is, ignoring the plus or minus sign -- indicates the strength of the relationship between X and Y.

• ### Measure of Relationship

• A correlation of +.95 or of -.95 indicates a very strong relationship between the two variables.

• A correlation of 0 indicates that there is no linear relationship between the variables.

• Guilford's suggested interpretations for values of r.

### Problems Effecting the Interpretation

• Non Linear Relationship

• Outliers