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