Hi Nicole, 

Given that the control group does not have the dose metric, you may want to consider a follow-up analysis  that only includes the active/patient group. The design matrix would include a columns of ones and column for your dose metric as well as any other covariates. The contrast would be [0 1] (postive correlation) or [0 -1] (negative correlation)

Another approach would be to include both groups and simply use a value of zero for the dose variable of the control group. But this might not make sense, depending on your context. 

Originally posted by Natalie Bell:

Hello,

I am trying to determine how to set up a follow-up analysis. I have significant findings between two groups and I want to see if these findings are dose dependent by adding in a quantative metric. I want to see specifically if there is a positive or negative correlation between one of the groups and this dose metric but the control group does not have this dose metric so I am wondering if this will be possible. How would I go about designing a linear regression model in the NBS accordingly? Would I keep only one group in the design matrix?