Table 2

Recruitment intervention and effect on participation

Recruitment interventionReference IDIncreasesDecreasesLittle impactInconclusive
Trial design
 Open design16 32
 Placebo* 59
 Patient preference design18
 Zelen design†25
 Internet-based data capture†42
Obtaining consent
 Process—opt-out approach55
 Process—consent to experimental treatment*48 50
 Process—consent to standard treatment*48 50
 Process—refuser chooses treatment option*50
 Process—physician modified chance of experimental*48
 Process—participant modified chance of experimental*48
 Form—researcher read aloud56
 Form—altered readability level†19
Approach to participants
 Delivery—video presentation*†28 35
 Delivery—video presentation plus written information60
 Delivery—audiovisual overview of trials21 22 33
 Delivery—interactive computer presentation*36 44
 Delivery—verbal education session45
 Supplementing info—booklet on clinical trials*23 34
 Supplementing info—study-relevant questionnaire31 37
 Supplementing info—newspaper article51
 Framing—treatment as faster*52
 Framing—treatment as new*38
 Framing—emphasis on pain or risk*54
 Framing—positively or negatively*43
 Content—more detailed info (inc. total disclosure)*27 53
 Content—financial disclosure of investigator interest*†57 58
 Telephone reminders31 49
 SMS messages26
 Eligibility screening—face-to-face*24 29
 Eligibility screening—telephone*20
 Eligibility screening—electronic self-complete*29
 Screening personnel46
Financial incentives
 Cash incentive with invitation26
 Paid participation*†17 30
 Level of trial risk*†17 30
Training for recruiters
 Training lay advocates†40
 Education sessions†39
Trial co-ordination
 On-site visits†41
 Additional communication†47
  • ●, Multiple studies; ⊙, single study.

  • *Includes recruitment to hypothetical trial(s).

  • †Includes result reported by study authors only (effect size not calculated).