Skip to main content

Table 2 Participant beliefs and voluntary run-in failure

From: Randomized controlled trials: who fails run-in?

 

Full factorial randomization

Two-group randomization

 

Men (N = 1606)

Women (N = 301)

Women (N = 666)

 

Randomized

Voluntary run-in failure

p

Randomized

Voluntary run-in failure

p

Randomized

Voluntary run-in failure

p

 

N (%)

N (%)

 

N (%)

N (%)

 

N (%)

N (%)

 
 

1423 (89)

183 (11)

 

252 (84)

49 (16)

 

584 (88)

82 (12)

 

BASELINE FACTORS

 Preference: If you could choose, which kind of pill would you like to receive during the study?

  Calcium + vitamin D

854 (90)

96 (10)

0.08

174 (87)

27 (13)

0.10a

450 (88)

62 (12)

0.37

  Calcium only

67 (83)

14 (17)

 

13 (65)

7 (35)

 

34 (81)

8 (19)

 

  Vitamin D only

63 (83)

13 (17)

 

8 (80)

2 (20)

 

N/A

N/A

 

  Placebo

32 (94)

2 (5.9)

 

4 (100)

0

 

N/A

N/A

 

  Don’t know/refused

407 (88)

57 (12)

 

53 (80)

13 (20)

 

99 (89)

12 (11)

 

  Missing

0

1 (100)

 

0

0

 

1 (100)

0

 

 Efficacy belief: How likely do you think it is that vitamin D supplements …

 Are helpful in preventing polyps

  

0.74

  

0.72

  

0.44

  Very/somewhat likely

852 (89)

108 (11)

 

173 (83)

36 (17)

 

381 (87)

58 (13)

 

  Don’t know

530 (89)

67 (11)

 

70 (86)

11 (14)

 

182 (89)

23 (11)

 

  Very/somewhat unlikely

40 (85)

7 (15)

 

8 (80)

2 (20)

 

20 (95)

1 (4.8)

 

  Refused/missing

1 (50)

1 (50)

 

1 (100)

0

 

1 (100)

0

 

 Improve health

  

0.20

  

0.42a

  

0.30

  Very/somewhat likely

1189 (89)

143 (11)

 

239 (84)

45 (16)

 

514 (87)

76 (13)

 

  Don’t know

177 (85)

31 (15)

 

10 (77)

3 (23)

 

56 (90)

6 (9.7)

 

  Very/somewhat unlikely

56 (88)

8 (13)

 

3 (75)

1 (25)

 

13 (100)

0

 

  Refused/missing

1 (50)

1 (50)

 

0

0

 

1 (100)

0

 

 Improve pain in bones and joints

  

0.59

  

0.63

  

0.18

  Very/somewhat likely

902 (89)

109 (11)

 

176 (83)

37 (17)

 

347 (86)

57 (14)

 

  Don’t know

374 (88)

51 (12)

 

44 (85)

8 (15)

 

184 (91)

18 (8.9)

 

  Very/somewhat unlikely

145 (87)

22 (13)

 

32 (89)

4 (11)

 

52 (88)

7 (12)

 

  Refused/missing

2 (67)

1 (33)

 

0

0

 

1 (100)

0

 

 Improve mood

  

0.31

  

0.47

  

0.06

  Very/somewhat likely

375 (87)

56 (13)

 

86 (83)

18 (17)

 

240 (84)

45 (16)

 

  Don’t know

632 (90)

71 (10)

 

89 (87)

13 (13)

 

245 (91)

25 (9.3)

 

  Very/somewhat unlikely

414 (88)

55 (12)

 

77 (81)

18 (19)

 

98 (89)

12 (11)

 

  Refused/missing

2 (67)

1 (33)

 

0

0

 

1 (100)

0

 

 Cause constipation

  

0.36

  

0.46

  

0.09

  Very/somewhat likely

240 (86)

38 (14)

 

82 (87)

12 (13)

 

117 (82)

25 (18)

 

  Don’t know

669 (89)

85 (11)

 

91 (83)

18 (17)

 

282 (90)

33 (10)

 

  Very/somewhat unlikely

511 (90)

59 (10)

 

79 (81)

19 (19)

 

184 (88)

24 (12)

 

  Refused/missing

3 (75)

1 (25)

 

0

0

 

1 (100)

0

 

 Efficacy scoreb mean (SD) compared with [randomized participants]

2.8 (2.6)

2.5 (2.9)

0.20

3.1 (2.5)

3.4 (2.7)

0.39

3.3 (2.6)

3.6 (2.9)

0.26

 Efficacy scoreb

  

0.16

  

0.94a

  

0.81

  −9 to −1 (benefit unlikely)

97 (85)

17 (15)

 

21 (88)

3 (13)

 

29 (88)

4 (12)

 

  0 (no benefit)

149 (85)

26 (15)

 

16 (80)

4 (20)

 

49 (89)

6 (11)

 

  1–5 (little benefit)

957 (90)

109 (10)

 

168 (84)

33 (16)

 

390 (88)

52 (12)

 

  6–10 (some benefit)

220 (88)

31 (12)

 

47 (84)

9 (16)

 

116 (85)

20 (15)

 

 Allocation belief: If you were to place a bet, which pill would you bet you’ll be given during the trial?

  Calcium + vitamin D

236 (90)

25 (9.6)

0.96

38 (83)

8 (17)

0.89a

116 (85)

21 (15)

0.73

  Calcium only

102 (89)

13 (11)

 

18 (82)

4 (18)

 

95 (88)

13 (12)

 

  Vitamin D only

91 (90)

10 (9.9)

 

11 (79)

3 (21)

 

N/A

N/A

 

  Placebo

206 (89)

25 (11)

 

31 (79)

8 (21)

 

N/A

N/A

 

  Don’t know/refused

150 (91)

15 (9.1)

 

18 (90)

2 (10)

 

29 (88)

4 (12)

 

  Missing/not askedc

638 (87)

95 (13)

 

136 (85)

24 (15)

 

344 (89)

44 (11)

 

POST-ENROLLMENT FACTOR

 Perceived toxicity during the run-in periodd

  No

1412 (89)

169 (11)

<0.0001a

249 (85)

43 (15)

0.001a

581 (89)

73 (11)

<0.0001a

  Yes

11 (44)

14 (56)

 

3 (33)

6 (67)

 

3 (25)

9 (75)

 
  1. Missing data are shown where values are not zero. p values are based on non-missing data
  2. aFisher exact test
  3. bEfficacy score was calculated as follows: For the first four health outcomes, extremely likely scores 2; somewhat likely scores 1; don’t know (or refused or missing) scores 0; somewhat unlikely scores –1; extremely unlikely scores –2. For constipation, the scoring system is reversed, e.g., very likely to cause constipation scores –2. All five scores are summed to give an overall efficacy score
  4. cThe number of respondents is smaller because this question was removed from the questionnaire
  5. dPerceived toxicities are defined as reports made by study coordinators on symptoms that participants attribute to the study tablets. These are identified either during the randomization questionnaire or if participants specifically contact study coordinators to report them
Back to article page

Trials

ISSN: 1745-6215