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Table 3 Missing data interventions and reported evaluations into their effectiveness (registered Clinical Trial Unit (CTU) survey Questions 6 and 7)

From: Identifying research priorities for effective retention strategies in clinical trials

Missing data intervention Respondents who have used the intervention (% of all survey respondents, n = 33) Used routinely (% of all survey respondents, n = 33) Used occasionally (% of all survey respondents, n = 33) No response for frequency of use (% of respondents who used intervention) Before/after evaluation (informal) Nested RCT evaluation (formal) Total evaluations
Newslettersa 30 (91%) 23 (70%) 5 (15%) 2 (7%) 2 2 4
A timeline of participant visits for sites 24 (73%) 19 (58%) 4 (12%) 1 (4%) 0 0 0
Inclusion of prepaid envelope (questionnaires)b 28 (85%)c 19 (58%) 6 (18%) 1 (4%) 0 1 1
Telephone reminders 28 (85%) 18 (55%) 9 (27%) 1 (4%) 2 1 3
Data collection scheduled with routine care 25 (76%) 18 (55%) 6 (18%) 1 (4%) 1 1 2
Site initiation training on missing data 19 (58%) 18 (55%) 0 (0%) 1 (5%) 0 0 0
Investigator meetings face to face 22 (67%) 17 (52%) 5 (15%) 0 (0%) 0 1 1
Routines site visits by CTU staff 23 (70%) 15 (45%) 8 (24%) 0 (0%) 1 0 1
Targeted recruitment of sites/GPs 21 (64%) 15 (45%) 6 (18%) 0 (0%) 0 2 2
Flexibility in appointment times 21 (64%) 15 (45%) 4 (12%) 2 (10%) 1 1 2
Communication of trial results 20 (61%) 15 (45%) 3 (9%) 2 (10%) 1 0 1
Investigator teleconferences 22 (67%)d 15 (45%) 8 (24%) 0 (0%) 0 1 1
Questionnaires completed in clinicb 22 (67%) 15 (45%) 5 (15%) 2 (9%) 1 1 2
Minimising frequency of questionnairesb 21 (64%) 15 (45%) 3 (9%) 3 (14%) 0 0 0
Short questionnaireb 24 (73%) 14 (42%) 9 (27%) 1 (4%) 0 1 1
Collecting multiple contact details 22 (67%) 13 (39%) 8 (24%) 1 (5%) 2 1 3
Email reminders 21 (64%) 13 (39%) 6 (18%) 2 (10%) 4 0 4
Postal reminders 23 (70%) 12 (36%) 10 (30%) 1 (4%) 2 2 4
Total design method for Questionnairesb 15 (46%) 12 (36%) 3 (9%) 0 (0%) 1 1 2
Re-imbursement of participant expenses 24 (73%)e 11 (33%) 12 (36%) 0 (0%) 1 1 2
Triggered site training on missing data 23 (70%) 11 (33%) 12 (36%) 0 (0%) 0 0 0
Use of routinely collected data 29 (88%) 10 (30%) 17 (52%) 2 (7%) 2 1 3
Contact GPs for missing data/trace patients 27 (82%) 10 (30%) 14 (42%) 3 (11%) 0 1 1
Patient diaries 26 (79%) 10 (30%) 13 (39%) 3 (12%) 1 0 1
Enhanced cover letter (questionnaires)b 14 (43%) 9 (27%) 5 (15%) 0 (0%) 1 2 3
Staggered per patient payments to sites 20 (61%) 8 (24%) 12 (36% 0 (0%) 0 0 0
Patient data entry 18 (55%) 8 (24%) 8 (24%) 2 (11%) 0 1 1
Trial identity cards 14 (43%) 8 (24%) 5 (15%) 1 (7%) 0 0 0
Telephone questionnaires 20 (61%) 7 (21%) 11 (33%) 2 (10%) 2 1 3
Trial website 18 (55%) 7 (21%) 10 (30%) 1 (6%) 0 0 0
Taking contact details for a friend/family 13 (40%) 7 (21%) 6 (18%) 0 (0%) 0 1 1
Long but clear questionnaireb 10 (31%) 7 (21%) 2 (6%) 1 (10%) 0 0 0
Only collecting the primary outcome for patients with missing data 17 (52%) 6 (18%) 10 (30%) 1 (6%) 2 1 3
Gift 18 (55%) 6 (18%) 10 (30%) 2 (11%) 1 1 2
ONS flagging 16 (49%)e 6 (18%) 7 (21%) 2 (13%) 0 0 0
Flexibility in appointment locations 14 (43%) 6 (18%) 6 (18%) 2(14%) 1 0 1
Money/gift voucher given on completion of a milestone 17 (52%) 5 (15%) 12 (36%) 0 (0%) 1 0 1
Contacting patients between visits 13 (40%) 4 (12%) 9 (27%) 0 (0%) 0 0 0
Christmas and birthday cards 13 (40%) 4 (12%) 9 (27%) 0 (0%) 0 1 1
Freephone number for updating contact 7 (22%) 4 (12%) 3 (9%) 0 (0%) 0 0 0
Follow-up through patient notes only 19 (58%)e 3 (9%) 15 (45%) 0 (0%) 0 0 0
Transport to and from appointments 8 (25%) 3 (9%) 4 (12%) 1 (13%) 0 0 0
SMS text reminders 16 (49%)e 2 (6%) 13 (39%) 0 (0%) 3 1 4
Trial certificate 8 (25%) 2 (6%) 6 (18%) 0 (0%) 0 0 0
Medical questions first in questionnaireb 2 (7%) 2 (6%) 0 (0%) 0 (0%) 0 0 0
Generic questions first in questionnaireb 3 (10%) 2 (6%) 0 (0%) 1 (33%) 0 0 0
Questionnaires sent less than 3 weeks after a visitb 2 (7%) 2 (6%) 0 (0%) 0 (0%) 0 0 0
Other (questionnaires) b 2 (7%) 2 (6%) 0 (0%) 0 (0%) 0 0 0
Money/gift voucher given regardless 8 (25%) 1 (3%) 7 (21%) 0 (0%) 1 2 3
Case management 3 (10%) 1 (3%) 2 (6%) 0 (0%) 0 0 0
Other 2 (7%) 1 (3%) 1 (3%) 0 (0%) 0 0 0
Personal touch (questionnaires)b 9 (28%) 1 (3%) 8 (24%) 0 (0%) 0 0 0
Questions about health issue first in questionnaireb 1 (4%) 1 (3%) 0 (0%) 0 (0%) 1 0 1
Questionnaires sent before clinic visitb 5 (16%) 1 (3%) 4 (12%) 0 (0%) 0 1 1
Prize draw limited to trial participants 6 (19%) 0 (0%) 6 (18%) 0 (0%) 0 0 0
Social media 5 (16%)e 0 (0%) 3 (9%) 1 (20%) 0 0 0
Priority or recorded post (questionnaires)b 4 (13%) 0 (0%) 3 (9%) 1 (25%) 0 0 0
Crèche service 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 0 0
Behavioural motivation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 0 0
Charity donation 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 0 0
National lottery ticket or similar public draw 0 (0%) 0 (0%) 0 (0%) 0 (0%) 0 0 0
Total 35 31 66
Number of strategies that have been evaluated (% of all strategies, n = 59) 23 (39%) 26 (44%) 36 (61%)
  1. aOne case where the newsletters were used with patients only, nine cases where newsletters were used with both patients and research sites, and 20 cases where they were only used with research sites. bStrategies used to enhance questionnaire response rates from Question 7 of the registered CTU survey cTwo respondent stated that they would not use this intervention again. dOne person reported both occasional and routine use. eOne respondent stated that they would not use this intervention again
  2. CTU Clinical Trial Unit, GP general practitioner, ONS Office for National Statistics, RCT randomised controlled trial, SMS short message service