CODEWITHSUNDEEP
sasbioinformatics
ybao
ybao

Reputation: 147

Logistic regression with ordinal explanatory variable

I have a set of data where I would like to do logistic regression modeling the odds of a binary outcome variable (Therapy), with Stage as an ordinal explanatory variable (0,1,2,3,4). Hba1c is a continuous variable.

Is my class statement correct?

How do I get it to calculate the odds ratios for each level of the ordinal variable?

PROC LOGISTIC data=new;
class EyeID Therapy (ref ="0") Stage (param = ordinal) Gender (ref="M") Ethnicity (ref="C")/ param = ref;
model Therapy = Stage Gender age A1c Ethnicity;
oddsratio Stage;
run;

This is the Output:

Odds Ratio Estimates and Wald Confidence Intervals
Odds Ratio  Estimate    95% Confidence Limits
Stage 1 vs 0    0.873   0.547   1.394
Stage 2 vs 0    2.434   0.895   6.620
Stage 3 vs 0    0.915   0.431   1.941
Stage 4 vs 0    0.356   0.132   0.961
Stage 2 vs 1    2.788   0.980   7.935
Stage 3 vs 1    1.048   0.465   2.360
Stage 4 vs 1    0.408   0.144   1.156
Stage 3 vs 2    0.376   0.113   1.249
Stage 4 vs 2    0.146   0.038   0.567
Stage 4 vs 3    0.389   0.117   1.288

If I am reporting Stage as an ordinal variable, then is it correct that I create a table like this?

Stage 1 vs 0    0.873   0.547   1.394
Stage 2 vs 1    2.788   0.98    7.935
Stage 3 vs 2    0.376   0.113   1.249
Stage 4 vs 3    0.389   0.117   1.288

I should not report it like this, correct? This is if stage was categorical?

Stage 1 vs 0    0.873   0.547   1.394
Stage 2 vs 0    2.434   0.895   6.62
Stage 3 vs 0    0.915   0.431   1.941
Stage 4 vs 0    0.356   0.132   0.961

Upvotes: 1

Views: 841

Answers (1)

DomPazz
DomPazz

Reputation: 12465

I do not think you need Therapy on the class statement.

Without sample data, I cannot test this, but my first pass would have been to write it like this.

proc logistic data=test;
class PVDStage (param = ordinal);
model Therapy(ref = '0') = PVDStage hba1c;
ODDSRATIO PVDStage;
run;

If you can provide some sample data, I will amend my answer to ensure it works.

Upvotes: 1

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