I am designing a study in which a large number of people are being treated. I cannot influence the treatment (e.g., a delayed treatment). I am able to make pre and post treatment measures on the subjects. The treatment has many effects on the subjects. I have a screener that I believe will identify subjects that will predict individuals that will improve on measure A.
The proposed experimental design is for two groups to be identified based on a screening test (the screening test can be administered pre or post treatment). Both groups will be subjected to the same treatment. Prior to and following treatment both groups will be tested on measures A and B. The hypothesis is that the treatment will effect the groups differently on measure A but not on measure B. Is there a term for this design? Is this a valid design?