RESEARCH METHODS HANDBOOK

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Contents	Introduction	Descriptive	Hypothesis	Tables	Appendix

Pearson's Product Moment Correlation Coefficient

Verify Conditions for using Pearson r

Interval/ratio data must be from paired observations.

A linear relationship should exist between the variables -- verified by plotting the data on a scattergram.

Pearson r computations are sensitive to extreme values in the data

Compute Pearson's r

n = number of paired observations

X = variable A

Y = variable B

Interpret the Correlation Coefficient A positive coefficient indicates the values of variable A vary in the same direction as variable B. A negative coefficient indicates the values of variable A and variable B vary in opposite directions.

Characterizations of Pearson r

.9 to 1 very high correlation
.7 to .9 high correlation
.5 to .7 moderate correlation
.3 to .5 low correlation
.0 to .3 little if any correlation Interpretation: There is a (insert characterization)(positive or negative) correlation between the variation of X scores and the variation of Y scores. Determine the Coefficient of Determination

Interpretation: _______ percent of the variance in ______ can be associated with the variance displayed in ______.

Example