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Table 1 Top 10 most used missing data strategies by CTUs in the UK [6]

From: How much is the lack of retention evidence costing trial teams in Ireland and the UK?

 

Missing data strategies

Number (N) and percentage of CTUs that routinely use strategies

Evidence of reported evaluations into their effectiveness according to the most recent Cochrane Systematic Review [9].

1

Newsletters

N=23, 70%

“The evidence is very uncertain about the effect on retention of including a newsletter compared to no newsletter; RD = − 0% (95%CI, − 4% to 3%); GRADE; very low”, evidence is based on four studies from various disciplines (n=5622)

2

A timeline of participant visits for sites

N=19, 58%

No evidence

3

Inclusion of prepaid envelopes (questionnaires)

N=19, 58%

“Various strategies compared to usual practice for return postage, such as free post versus second class stamp, high priority mail stamp versus usual postage and personal form may increase retention slightly: RD= 4% (95% CI − 0% to 9%), GRADE; low”. Evidence is based on three studies, (n=1543)

4

Telephone reminders

N=18, 55%

“Telephone reminders compared to postal reminders may result in a large increase in retention, evidence is from one study [10] (RD= − 19% (95%CI − 33% to − 5%) GRADE low (− 1 level: study limitations unclear risk of bias; − 1 level: imprecision single study, n=148)”

“Telephone reminders compared to usual follow-upa may result in little or no difference in retention, (smoking cessation [11] (RD = − 1% (95% − 18% to 15%) GRADE low, (− 2 levels: imprecision-single study, n = 127; wide CI crossing RD = 0))” b

5

Data collection scheduled with routine care

N=18, 55%

No evidence

6

Site initiation training on missing data

N=18, 55%

No evidence

7

Investigator meetings face to face

N=17, 52%

No evidence

8

Routine site visits by CTU staff

N=15, 45%

No evidence

9

Targeted recruitment of sites/GPs

N=15, 45%

No evidence

10

Flexibility in appointment times

N=15, 45%

No evidence

  1. GRADE, grades of evidence; low certainty: the confidence in the effect estimate is limited; the true effect may be substantially different from the estimated effect. Very low certainty: very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of the effect [9]
  2. aFrom this single study “usual follow-up” is as follows; “We followed-up participants by any of the means they agreed to at the start of the trial, including post, e-mail, and telephone calls to mobile, home, or work numbers [12]. We used all the effective evidence-based methods that were feasible to introduce into the procedures of the trial [12], as identified in the systematic reviews by Edwards et al. and Hoile et al. [13]. These included monetary incentives, posting correspondence by recorded delivery, pre-notification, follow-up contact, unconditional advance cash incentives, short, concise questionnaires, duplicate questionnaires sent at repeat follow-up attempts, mentioning that commitment to the trial implied an obligation to respond, mention of university sponsorship, prepaid return envelopes with stamps, an assurance of confidentiality, and first-class outward mailing” [11]
  3. bWe present all evidence regarding telephone reminders however we chose to select telephone reminders compared to the usual follow-up in Table 4 to calculate the cost per participant retained as we believe it is the most relevant comparison for trial teams
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Trials

ISSN: 1745-6215