What is the best method for testing for lack of fit in models fit using Proc Mixed? I'm running models testing effects of river reach, forest stand age, elevation above the river, and distance from the river on soils in riparian forests. Samples were collected from plots located within distinct forest patches, arrayed along randomly located transects within each river reach, so I include patch nested within transect and transect nested within reach as random effects. I've pasted the code below. I'm running these models to assess the relative importance of stand age, elevation, and distance by comparing AICc scores among models that include different combinations of the variables. I'd like to have a method to check whether the "best model" (i.e., the model with the lowest AICc) provides a good fit to the data. Thanks in advance for any advice. - Laura title soilN - age elev dist; proc mixed; class reach transect patch; model N=age elev dist reach / solution ddfm=kenwardroger; random transect(reach) patch(transect*reach); run;
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