Betty,
The drug study should, and probably does, do random assignment. Which means that everyone in the study has an equal chance of being in either condition (experimental condition = Enbrel, control condition = placebo). This ensures the validity of the study. I hope this makes some sense, you might want to do some research on experimental procedures in general for more information on how these studies are done.
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Kristin TODAY IS NOT A DRESS REHEARSAL!! 
