Table 2 Associations between enrollment rate and trial characteristics of the 289 included randomized controlled trials—univariate analysis

Funding source

0.096

 Industry

80 (28)

39 (27–51)

 Others

209 (72)

42 (27–58)

Country classification

0.448

 Developed economies

170 (59)

39 (25–54)

 Developed and developing economies

33 (11)

42 (32–54)

 Developing economies

86 (30)

41 (28–54)

Age

< 0.001

 Quartile 1 (≤ 45)

71 (24)

47 (30–64)

 Quartile 2 (46–55)

72 (25)

46 (33–58)

 Quartile 3 (56–62)

76 (26)

38 (27–50)

 Quartile 4 (≥ 63)

70 (24)

33 (20–46)

Type of intervention

< 0.001

 Invasive

55 (19)

31 (22–46)

 Non-invasive

234 (81)

42 (29–58)

Type of comparison

0.357

 Drug vs. drug

95 (33)

38 (24–50)

 Drug vs. placebo

63 (22)

42 (29–58)

 Others

131 (45)

44 (28–54)

Setting

0.898

 Inpatients

55 (19)

37 (27–46)

 Outpatients

234 (81)

42 (27–58)

Type of primary outcome

< 0.001

 Hard

34 (12)

35 (26–47)

 Surrogate

125 (43)

38 (23–53)

 Soft

130 (45)

44 (30–59)

Adequate sequence generation

211 (73)

42 (27–58)

0.113

Allocation concealment

189 (65)

42 (28–59)

0.188

Blinding

0.135

 Single or no blinding

181 (63)

40 (27–53)

 Double or triple

108 (37)

42 (27–56)