How to: Graphing nonlinear regression curves

Automatic vs. manual plotting

When Prism performs nonlinear regression, it automatically superimposes the curves on the graph.

If you need to create additional graphs, or change which curve is plotted on which graph, keep in mind that from Prism's point of view, a curve generated by nonlinear regression is simply a data set. You can add curves to a graph or remove curves from a graph on the 'Data on graph' tab of the Format Graph dialog.

Plotting curves after comparing models

If you ask Prism to compare two models, only the selected model is graphed. If you want to graph both models, you will need to analyze the data twice, once with each model.

Prism 5 plots curves differently than did early versions

If you have used earlier versions of Prism, beware of these two differences:

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With Prism 5, it is Ok to stretch an axis to a log scale, a choice on top of the Format Axis dialog. With prior versions, this didn't work well. The curve was defined as a series of line segments, and these would be far from equally spaced on a log axis. Prism 5 makes it work, so the curve will look smooth on either a linear or logarithmic axis.

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Prism plots the curve by drawing a set of small line segments. In earlier versions of Prism, you chose how many segments Prism should create. Prism 5 decides this automatically. If you want to create a table of XY coordinates for exporting, you decide how many rows this table should have, but that choice only matters for creating the table and has no impact on how the curve is plotted.