In statistics, we often use the Pearson correlation coefficient to measure the linear relationship between two variables.
However, sometimes we’re interested in understanding the relationship between two variables while controlling for a third variable.
For example, suppose we want to measure the association between the number of hours a student studies and the final exam score they receive, while controlling for the student’s current grade in the class.
In this case, we could use a partial correlation to measure the relationship between hours studied and final exam score.
This tutorial explains how to calculate partial correlation in SPSS.
Example: Partial Correlation in SPSS
Suppose we have a dataset that shows the following information for 10 students:
- Current grade in a class
- Hours spent studying for the final exam
- Final exam score
Perform the following steps to calculate the partial correlation between hours and exam, while controlling for grade:
- Click the Analyze tab.
- Click Correlate.
- Click Partial.
In the window that pops up, drag hours and exam into the box that says Variables and drag grade into the box that says Controlling for. Then click OK.
Once you click OK, the following screen will appear:
We can see that the partial correlation between hours studied and final exam score is .191, which is a small positive correlation. As hours studied increases, exam score tends to increase as well, assuming current grade is held constant.
The corresponding two-tailed p-value is .623. Since this value is not less than 0.05, this means the partial correlation between hours and exam score is not statistically significant.