1.	controlled clinical trial.pt.
2.	randomized controlled trial.pt.
3.	randomized controlled trials/
4.	random allocation/
5.	double blind method/
6.	single blind method/
7.	clinical trial.pt.
8.	exp clinical trials/
9.	placebos/
10.	placebo$.tw.
11.	random$.tw.
12.	research design/
13.	volunteer$.tw.
14.	(clin$ adj25 trial$).tw.
15.	((singl$ or doubl$ or trebl$ or tripl$) adj25 (blind$ or mask$)).tw.
16.	factorial.tw.
17.	cross‐over studies/
18.	crossover.tw.
19.	latin square.tw.
20.	(balance$ adj2 block$).tw.
21.	(animals not humans).sh.
22.	or/1‐20
23.	22 not 21
24.	exp clinical trial/
25.	clinical trials as topic/ or clinical trials, phase i as topic/ or clinical trials, phase ii as topic/ or clinical trials, phase iii as topic/ or clinical trials, phase iv as topic/ or controlled clinical trials as topic/ or randomized controlled trials as topic/ or multicenter studies as topic/
26.	or/1‐20,24‐25
27.	26 not 21
28.	urethrotom$.tw.
29.	(dilatat$ adj25 urethra$).tw.
30.	self dilatat$.tw.
31.	urethroplast$.tw.
32.	urethral stricture/
33.	(urethra$ adj5 (stricture$ or stenos$)).tw.
34.	or/28‐33
35.	34 and 27