This operation is only available in the right-click menus of scatterplot trellis displays and sum-difference plot trellis displays. What it does depends on if there is a ✓ mark to its left in a right-click menu.
It adds a trend line to the point cloud in each panel of a trellis display. These trend lines are computed by linear regression with the variable on the vertical axis as the dependent variable and the variable on the horizontal axis as the independent variable.
If the Shift key is pressed when this operation is invoked, the regression line in each panel is forced to go through the origin; otherwise, a constant intercept term is estimated.
If a trellis display has any panel plots, this operation will add a linear regression line to each of them, too. Unlimited panel plots won't be affected.
Linear regression lines are already being displayed in the trellis display on which this operation is invoked and in any associated panel plots. This operation will remove all these linear regression lines.