Setting up a general linear model with multiple comparisons or contrasts

BlueNose — Fri, 03 Aug 2018 14:50:51 GMT

Dear all,

I have data containing one dependent variable, I'll call it Y for simplicity, and let's assume it is normally distributed.

I have independent variables X1, X2, X3, X4. All of them are ordinal, getting values of 1-4, where 4 is highest and 1 lowest. In addition, I have some covariates, such as age, gender, etc...

I wish to model Y vs. the independent variables and the covariates, but I am mostly interested in finding if there are significant differences between groups 1 and 4 of each independent variable.

Using the following code:

PROC GLM DATA = Dat;
    CLASS X1;
    MODEL Y = X1 Age Gender ;
    LSMEANS X1 / cl pdiff diff;
RUN;

Gives me a linear model, with multiple comparisons of all pairs of the variable X1.

Is there a better way to model in this situation ? Is there a way to define something like a contrast, so only groups 1 and 4 will be compared with higher power ? Is my code correct in the first place ?

Thank you in advance !

Re: Setting up a general linear model with multiple comparisons or contrasts

PaigeMiller — Fri, 03 Aug 2018 14:53:42 GMT

Use the CONTRAST statement in PROC GLM

http://documentation.sas.com/?cdcId=pgmmvacdc&cdcVersion=9.4&docsetId=statug&docsetTarget=statug_glm_syntax06.htm&locale=en

topic Setting up a general linear model with multiple comparisons or contrasts in Statistical Procedures

Setting up a general linear model with multiple comparisons or contrasts

Re: Setting up a general linear model with multiple comparisons or contrasts