A randomized clinical trial has 4 treatment groups (1:1:1:1 randomization to placebo, dose level 1, dose level 2, and dose level 3), and there is interest in understanding the following treatment comparisons:
- dose level 1: placebo
- dose level 2: placebo
- dose level 3: placebo
- any active dose: placebo
For the “any active dose to placebo” comparison, one could fit a separate model where treatment group is coded to 2 levels, or one could extract the comparison from the same model where treatment group is coded to 4 levels via a separate ESTIMATE statement in SAS. Note that the two approaches will give slightly different estimates and p values due to the different degrees of freedom.
- What are the pros and cons of either approach, or is one preferred over the other? What is the rationale of the latter approach other than convenience (or perhaps efficiency)?
- Would interpretation differ for the two approaches?
- Are there any references that discuss this?