Table 2.
Participant beliefs and voluntary run-in failure
| 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) | |||
Missing data are shown where values are not zero. p values are based on non-missing data
aFisher exact test
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
cThe number of respondents is smaller because this question was removed from the questionnaire
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