Establishing reference group/level in Proc Quantreg

[CaraJ]

Hello, I am running a quantile regression and do not want to use the standard options associated with the ORDER=statement in QUANTREG. I would instead like to establish my own reference/comparison group-is there a way currently to do this with the QUANTREG method?

Thank you

proc quantreg data=dataset ci=resampling (nrep=500); by Pathogen; class commodity;

model ill=commodity/quantile=0.25 0.5 0.75 plot=quantplot;

run;

[lvm]

Unlike with some other PROCs (e.g., LOGISTIC), QUANTREG does not have an option to change the reference level in the CLASS statement. You will have to use the ORDER= option.

[CaraJ]

Hi Ivm, I was afraid of that. Is there a way I could use a format feature possibly to use the default of ORDER=Formatted? Thank you

[lvm]

My approach would be to create a new variable in a data step, to be used as the CLASS variable. If you are using a character variable, the reference level should start with a "z" or "zz" so that it is the last one.

[CaraJ]

Thank you so much-I like that idea.

[1zmm]

Create a new format value for the CLASS variable you want to specify a reference level for.  For example, if "Barley" is the commodity you want as your reference level for all your commodities, use a PROC FORMAT VALUE statement to create a formatted value that sorts at the end of all formatted values by preceding that value with one or more right braces ("}"): 

   proc format;

       value $comm "Barley"="}} Barley";

   run;

   proc quantreg . . . order=formatted;

       class commodity;

       . . . .

       format commodity $comm.;

   run;

This syntax will make "Barley" the reference level for the classification variable, commodity.