topic Re: Establishing reference group/level in Proc Quantreg in Statistical Procedures

Establishing reference group/level in Proc Quantreg

CaraJ — Mon, 03 Jun 2013 20:27:19 GMT

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;

Re: Establishing reference group/level in Proc Quantreg

lvm — Tue, 04 Jun 2013 00:18:40 GMT

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.

Re: Establishing reference group/level in Proc Quantreg

CaraJ — Tue, 04 Jun 2013 13:26:30 GMT

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

Re: Establishing reference group/level in Proc Quantreg

lvm — Tue, 04 Jun 2013 13:32:47 GMT

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.

Re: Establishing reference group/level in Proc Quantreg

CaraJ — Tue, 04 Jun 2013 14:14:43 GMT

Thank you so much-I like that idea.

Re: Establishing reference group/level in Proc Quantreg

1zmm — Wed, 05 Jun 2013 11:30:34 GMT

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.