Thank you for this. I now realize that حجب is of course like in حجاب - cover :)
Now, where is the مشارك in your translation :) ? How about saying this -
"Randomized study, in which the nature of the medicine taken by the participant is concealed from the patient and investigator".
See fourth paragraph here for "concealed" -
http://www.ahrp.org/infomail/04/07/22.phpAlso, FYI - I understand that "investigator" is more commonly used than "researcher", even though the latter is probably the more literal. See, for example,
http://clinicaltrials.gov/ct2/show/NCT01398631?term=heart&ra... - towards the end of the document.
Thanks for your time and insight :)