Design of experiments across the time

#1
Hi all,

I am trying to model a continous variable across the time with several timepoints (0,3,6,9 and 12 months) and 2 predictors.

One is continuous (5 and 10) and the other is categorical (A, B and C) and for each of the combinaison I have 30 replicates.

The relation between Y and the time is not expeted to be linear. My main concern is to study the behavior of Y along the time and see if the 2 predictors included in the experiment have an influence.

Which statistical methodology/SAS procedure would you recommend?

Here is what I've used so far (SAS CODE):


ODS GRAPHICS ON;
PROC GLM DATA=STUDY PLOTS=ALL;
CLASS Component;
MODEL Y = Timepoint Timepoint*Timepoint Component FillingCoefficient FillingCoefficient*Timepoint Timepoint*Component / SOLUTION;
OUTPUT OUT=STUDY_results PREDICTED=pred RESIDUAL=res COOKD=Dcook RSTUDENT=rstud;
RUN;


Thanks in advance.

Cédric.
 

hlsmith

Not a robit
#3
How many unique units (subjects) do you have? You need to control for the within and between group variance - if I am following your descriptions. Thus you need to move over to PROC MIXED and use the REPEATED statement. Check it out and post further questions if they arise.
 
#4
I have 900 unique units. As the test to measure Y is destructive, at each timepoint 180 units are tested (30 for each combination). That's why I am wondering if using REPEATED statement is allowed in this case. Anyway I will get to PROC MIXED and keep you informed.

Sorry @Miner these data cannot be shared.