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.
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