26 19 and 25
27 controlled clinical trial/ or randomized controlled trial/ or “controlled clinical trial (topic)”/
28 randomization/
29 control group/
30 exp clinical trial/ or “clinical trial (topic)”/ or clinical study/ or “controlled clinical trial (topic)”/ or “multicenter study (topic)”/ or
“phase 1 clinical trial (topic)”/ or “phase 2 clinical trial (topic)”/ or “phase 3 clinical trial (topic)”/ or “phase 4 clinical trial (topic)”/
31 double blind procedure/
32 single blind procedure/
33 placebo/
34 palcebo effect.mp.
35 crossover procedure/