20. clinical trials as topic/ or clinical trials, phase i as topic/ or clinical trials, phase ii as topic/ or clinical trials, phase iii as topic/ or
clinical trials, phase iv as topic/
21. double-blind method/
22. single-blind method/
23. Placebos/
24. placebo effect/
25. cross-over studies/
26. Multicenter Studies as Topic/
27. Therapies, Investigational/
28. Research Design/
29. Program Evaluation/
30. evaluation studies as topic/