You may not even need a new variable. Consider:
proc format library=work;
value $sev
"Normal" ="Normal"
"Mild" ="Mild"
"Moderate"="Moderate"
"Moderately Severe","Severe"="Severe"
;
run;
proc freq data=nalergy.phq9;
table PHQ_9_Severity ;
format PHQ_9_Severity $sev.;
run;
Groups created by format levels are honored by almost all of the SAS analysis, reporting or graphing procedures.
One big advantage of custom format like this is that you do not need to keep adding variable. If latter you want to analyze on three groups such as "Normal" "Mild/Moderate" and "Moderately Severe/Sever" or "Normal" "Mild" "Moderate/Moderately Severe" "Severe" you only need to create a new format.
Another advantage is if you have multiple variables that have the same coding scheme you can apply the format to those variables as well with a single format statement. Or if you need the different levels in analysis then one format to one variable and a different to others.
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