Table 1 General characteristics of the population and methodological characteristics of the studies included in the review

N studies

77

8

2

20

3

108

89

4

311

sample size

6155

506

289

1192

105

4537

4221

303

17,308

mean age (years)

35.6

30.9

61.5

41.3

50.5

32.5

29.8

17

37.4

Male

(%)

1609

(26.1)

424

(83.8)

8

(2.8)

314

(26.3)

29

(27.6)

1712 (37.7)

1772

(42.0)

185 (61.1)

6053

(35.0)

- Parallel

74

8

2

19

2

79

76

4

264

- Crossover

3

0

0

1

1

29

13

0

47

PROM (yes)

29

1

2

11

0

39

24

3

109

PROM (no)

35

4

0

7

1

40

47

1

135

PROM (both)

13

3

0

2

2

29

18

0

67

Operator dependent measurements ( yes)

10

1

0

9

0

26

21

1

68

Operator dependent measurements (no)

65

6

2

7

1

71

63

3

218

Operator dependent measurements (both)

2

1

0

4

2

11

5

0

25

Blinding (double)

15

2

1

7

1

43

15

2

86

Blinding (single)

35

3

0

6

2

36

29

1

112

Blinding (not declared)

27

3

1

7

0

29

45

1

113

Source of enrolment (yes)

56

7

2

15

3

77

65

3

228

Source of enrolment (NR)

21

1

0

5

0

31

24

1

83