How to Draw a Regression Line in SPSS?
Our data basically just hold job performance scores and IQ, motivation and social support which -supposedly- contribute to job performance. The meaning of our variables is seen under variable view, part of which is shown below.
For these data, we'd normally inspect all predictors simultaneously by means of multiple regression. This tutorial, however, will be limited to the relation between motivation and job performance. That is, we'll ignore IQ and social support for now.
Regression Line Step 1: Scatterplot
So what does the relation between job performance and motivation look like? The best way to find out is running a scatterplot of these two variables as shown below. After doing so, we'll add a linear regression line to our plot to see whether it reasonably fits our data points.
As shown below, we usually plot the data values of our dependent variable on the y-axis. You could throw in a title at this point but we'll skip that for now.
SPSS Basic Scatterplot Syntax
Completing the steps shown in the previous screenshots results in the syntax below.
/SCATTERPLOT(BIVAR)=mot WITH perf
Step 2: Adding the Regression Line
Double-clicking our scatterplot in the Output Viewer window will open it in a Chart Editor window. Navigating to immediately adds the desired regression line to our scatterplot. We don't have to change any of the default settings; we can just the dialog.
For a prettier chart, you could manually style it somewhat -again, double-click it for opening the Chart Editor. We tried to create an SPSS chart template for styling our scatterplot with a regression line but the newly added elements weren't affected by it so it didn't work.
But are the Results Correct?
The ease with which we added our regression line without actually running REGRESSION made us a bit suspicious about the results. The syntax below -generated from- should yield a regression equation identical to the one in our scatterplot.
/STATISTICS COEFF OUTS R ANOVA
We find the R square value in our scatterplot in the Model Summary table (keep in mind that we usually prefer R square adjusted instead).
, The unstandardized coefficients in our Coefficients table also correspond to our scatterplot. We can be confident about the regression line we added to it.