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coby18
Calcite | Level 5

So apparently SAS likes to use the last variable as the reference variable for logistic regressions. All of my variables are coded as one would expect, with the smallest/first variable as the reference, so I would like to override this odd SAS default. I've figured out that I can use (ref=first) next to variables listed next to CLASS in order to account for my binary variables (0=no, 1=yes) but I'm not sure how to account for my continuous variables.

 

Here is the present state of my code for reference:

PROC SURVEYLOGISTIC DATA=brfss19s.brfss19shortvar;
CLUSTER _PSU;
CLASS DIABETE42 (ref=first)  SOFEMALE2 (ref=first);
MODEL DIABETE42 = ACETOTAL _AGE80 SOFEMALE2;
STRATA _STSTR;
WEIGHT _LLCPWT;
run;

 

Where ACETOTAL and _AGE80 are continuous variables that should be ordered normally (instead of using the highest value as the reference). 

 

Any guidance to address this hurdle would be greatly appreciated!!

 

P.S. I believe I'm using SAS 9.4

2 REPLIES 2
gcjfernandez
SAS Employee

For interval (continuous) independent variables the odds ratio is the change in Odds when you change the continuous variable by one unit while keeping all other continuous variables at constant level. You don't specify a reference levels.

StatDave
SAS Super FREQ

To be specific, the default odds ratio provided is the change in odds for a unit increase in the associated continuous predictor. You can specify what size increase or decrease in the predictor you want the odds ratio for by specifying the size in the UNITS statement. Similarly, the parameter estimate for a continuous predictor is the increase in the logit (log odds) for a unit increase in the predictor.

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