Why is my regression line too short (or too long)?

Prism's default method is to plot a regression line over the range of your input data.

• For a linear regression line, Prism 3.00 (Windows), by error, defaults to drawing the line from X=0 to X=100. If your data has a very different range, your graph will look odd. To fix the problem, click "Change.. "Analysis parameters". In the output options section of the Parameters dialog, set the appropriate minimum and maximum X values. Or check "Auto", and Prism will make the line extend from your first to last data points. In the future, set these auto settings every time you perform linear regression (or use a template or method with these settings in place). This problem was fixed in Prism 3.02. Prism 3.00-3.01 owners can update to version 3.03 free.
• If you want Prism to extend a regression line beyond the range of your input data, say, to the X and/or Y axis, the solution is the same: manually adjust the X value range. For linear regression, see the directions above. For nonlinear regression, click "Output.." in the Parameters dialog and set the range of X values in the resulting "Nonlinear regression output options" dialog.