15:56 Jul 26, 2011 

I think it's ok to omit the participant (مشارك). Probably just to be on the safer side and since you're dealing with homework, it might be better to include it. Besides, some clients want every word translated whenever possible.

The purpose of my translation earlier was to explain to you what the arabic sentence meant.

15:46 Jul 26, 2011 

I understand. So, if I do go with "administered", I trust it's OK to omit the participant (مشارك), as you did?

04:22 Jul 26, 2011 

My 2¢ and out of 4 years as a medical translator and quality assurance specialist of medical translations, I am fine with your translation except for the word investigator. investigator = مُحَقِّق whereas researcher = باحث.
As for the other terms, it really depends on who your audience is. If translating to address medical professionals, I would use "administered to participants" instead of "taken by participants" and "not disclosed to" instead of "concealed from".
The word conceal, in my opinion could convey malicious intentions just like in "xyz drug company was being investigated for concealing side effects of its abc medicine"

04:10 Jul 26, 2011 

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.php
Also, 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 :)