Table 1 Summary table showing the main study characteristics of 2019 papers split by randomisation method

Unit of Allocation

Individual

348 (90)

Cluster

37 (10)

If Cluster, Number of Clusters

2–25

15 (40)

26–50

8 (22)

51 + 

14 (38)

For individually randomised studies ^a

(n = 330)

(n = 20)

(n = 33)

(n = 66)

(n = 162)

(n = 49)

Number of Arms

2

270 (82)

16 (80)

30 (91)

51 (77)

128 (79)

45 (92)

3

39 (12)

3 (15)

1 (3)

14 (21)

18 (11)

3 (6)

4

15 (4)

0

1 (3)

1 (2)

12 (7)

1 (2)

5 + 

6 (2)

1 (5)

1 (3)

0

4 (3)

0

Number of Centres ^b

Single Centre

27 (8)

4 (20)

5 (15)

4 (6)

13 (8)

1 (2)

2–10

81 (25)

4 (20)

11 (34)

10 (15)

51 (31)

5 (10)

11–25

65 (20)

7 (35)

4 (12)

4 (6)

40 (25)

10 (20)

26–50

45 (14)

1 (5)

4 (12)

13 (20)

13 (8)

14 (29)

51–100

39 (12)

1 (5)

4 (12)

11 (17)

15 (9)

8 (16)

101 + 

70 (21)

3 (15)

5 (15)

24 (36)

27 (17)

11 (23)

Median (IQR)

22 (7, 86)

15 (4, 29)

11 (4, 51)

61 (17, 153)

16 (6, 53)

42 (14, 90)

Mean (SD)

72 (144)

59 (127)

121 (324)

111 (137)

51 (97)

62 (64)

Size of Study

< 200

60 (18)

6 (30)

10 (30)

15 (23)

23 (14)

5 (10)

201–1000

159 (48)

9 (45)

15 (46)

26 (39)

86 (53)

24 (49)

1001–10,000

103 (31)

4 (20)

6 (18)

24 (36)

49 (30)

20 (41)

10,001 + 

8 (3)

1 (5)

2 (6)

1 (2)

4 (3)

0

Median (IQR)

648 (241, 1468)

354 (133, 1445)

417 (154, 782)

690 (225, 1672)

653 (253, 1326)

694 (334, 2135)

Mean (SD)

1702 (3835)

1493 (2910)

1845 (3980)

1844 (3275)

1748 (4581)

1346 (1343)

Blinding

No

194 (59)

9 (45)

18 (55)

19 (29)

113 (70)

35 (71)

Yes

136 (41)

11 (55)

15 (45)

47 (71)

49 (30)

14 (29)