Plotting effects in original units

Dear Mariano,

The objects returned by the Effect() function, which is called repeatedly by allEffects(), contains all the information you need to create a custom plot. The fitted values for each effect on the scale of the linear predictor (i.e., not transformed to the scale of the response) -- that is, e.g., on the logit scale rather than the probability scale for a logit model --  are in the 'fit' component of the object. As I understand it, this is what you want to plot. The object also contains the combinations of values of the predictors at which the fit was evaluated in the 'x' component. Similarly, the confidence limits are in 'lower' and 'upper', also on the scale of the linear predictor. See ?Effect for more information about the returned object.

As to plotting on the original scales of the predictors rather than the standardized scales, you should be able easily to back-transform each predictor. But why bother? Why not just fit the model with the unstandardized predictors?

Finally, although the print() method for effect objects by default transforms effects to the scale of the response, and the plot() method plots on the scale of the linear predictor but labels the response axis on the scale of the response, you can modify this default behaviour. See ?print.eff and ?plot.eff (and in particular the type argument).

I hope this helps,
 John

-----------------------------
John Fox, Professor
McMaster University
Hamilton, Ontario
Canada L8S 4M4
web: socserv.mcmaster.ca/jfox

Plotting effects in original units

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