KNOWLEDGEBASE - ARTICLE #2003

How to create a table and graph of residuals when you fit a model to data using robust nonlinear regression?

If you check the option on the first tab of Prism's nonlinear regression dialog to set the fitting method to "robust", Prism then grays out (makes unavailable) the choice on the Diagnostics tab to create a table and graph of the residuals. Likewise, the choices to do normality tests and runs/replicates tests are also gray. But it can make sense to want to see residuals from the robust fit. At some point, we'll fix Prism. For now, use this dimple workaround:

  • On the first tab, check the option to do a regular least squares fit and choose your model. 
  • Go to the Diagnostics tab, and check the option to create a table and graph of residuals. And/or choose the runs test, replicates test or normality tests. 
  • Go back to the first tab, and check the option to do a robust fit. 
  • Click OK. And Prism will do a robust fit and report the residuals (and runs/replicates/normality tests)

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